Supplement no. 3 to prospectus dated August 7, 2006, and
prospectus supplement dated August 7, 2006

Filed Pursuant to Rule 424(b)(7).
A filing fee of $12,373.27, calculated in accordance with Rule 457(r), has
been transmitted to the SEC in connection with the securities
offered from the registration statement (File No.333-136361) by
means of this supplement to prospectus supplement.

$115,638,000
1.50% Convertible Senior Notes due 2011
1.625% Convertible Senior Notes due 2013
Common Stock

     This supplement no. 3 to prospectus dated August 7, 2006 and prospectus supplement dated August 7, 2006 relates to the resale by certain selling securityholders of our 1.50% Convertible Senior Notes due 2011 and 1.625% Convertible Senior Notes due 2013, which we refer to as the notes, and the shares of our common stock issuable upon conversion of the notes.

     You should read this supplement no. 3 in conjunction with the prospectus dated August 7, 2006, the prospectus supplement dated August 7, 2006, supplement no. 1 dated August 18, 2006 to the prospectus and the prospectus supplement, and supplement no. 2 dated September 7, 2006 to the prospectus and the prospectus supplement, or the prior registration documents, which should be delivered in conjunction with this supplement no. 3. This supplement no. 3 is not complete without, and may not be delivered or used except in conjunction with, the prior registration documents, including any amendments or supplements to them. This supplement no. 3 is qualified by reference to the prior registration documents, except to the extent that the information provided by this supplement no. 3 supersedes or supplements certain information contained in the prior registration documents.

     Investing in the notes and the common stock issuable upon conversion of the notes involves risk. See “Risk Factors” beginning on page 4 of the prospectus supplement dated August 7, 2006 (as amended by the last two paragraphs of this supplement no. 3).

     Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this supplement no. 3 or the prior registration documents. Any representation to the contrary is a criminal offense.

     This supplement no. 3 constitutes the offer by the selling securityholders named below of $41,727,000 principal amount of our 1.50% Convertible Senior Notes due 2011, or 2011 Notes, $73,911,000 principal amount of our 1.625% Convertible Senior Notes due 2013, or 2013 Notes, and the shares of our common stock issuable upon conversion of those notes.

     The table under the caption “Selling Securityholders” beginning on page 43 of the prospectus supplement (as previously amended and supplemented by the tables under the captions “Additional Selling Securityholders” and “Revised Information Regarding Securityholders” beginning on page 2 of supplement no. 1 dated August 18, 2006 to the prospectus and prospectus supplement and page 2 of supplement no. 2 dated September 7, 2006 to the prospectus and prospectus supplement) is hereby:

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supplemented by adding the information regarding certain selling securityholders set forth in the table entitled “Additional Selling Securityholders” below; and

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amended by replacing the information in the prospectus supplement, supplement no. 1 to the prospectus and prospectus supplement and supplement no. 2 to the prospectus and prospectus supplement regarding the selling securityholders identified in the table entitled “Revised Information Regarding Selling Securityholders” below with the information set forth in the table entitled “Revised Information Regarding Selling Securityholders” below.

     We prepared these tables based on information supplied to us by the selling securityholders named in the tables below on or prior to September 29, 2006. Information about the selling securityholders may change over time.

     We have assumed for purposes of the tables below that the selling securityholders will sell all of the notes and all of the common stock issuable upon conversion of the notes pursuant to this supplement no. 3 and the prior registration documents, and that any other shares of our common stock beneficially owned by the selling securityholders will continue to be beneficially owned.

     Except as set forth below, none of the selling securityholders has, or within the past three years has had, any position, office or other material relationship with us or any of our predecessors or affiliates.

     The selling securityholders identified below may have sold, transferred or otherwise disposed of, pursuant to transactions exempt from the registration requirements of the Securities Act of 1933, as amended, all or a portion of their notes since the date on which they provided the information regarding their notes.

Selling Securityholders

Additional Selling Securityholders

		Principal Amount of 2011								Principal Amount of 2013												Number of Shares of
		Notes Beneficially Owned								Notes Beneficially Owned												Common Stock
		and Offered (USD) and								and Offered (USD) and								Number of Shares of				Beneficially Owned				Natural Person(s)
Name of Selling		Percentage of 2011 Notes								Percentage of 2013 Notes								Common Stock				after the Offering				with Voting or
Securityholder (1)		Outstanding (%)								Outstanding (%)								Offered (2) (3)				(4)				Investment Power
Bear Stearns International Limited			20,000,000				*				15,000,000				*				623,396				—				(6)
Cowen & Company, LLC (#)			317,000				*				—				—				5,646				—				(5)
Fortis Investments Convertible Arbitrage			7,500,000				*				—				—				133,585				—				Kris Deblander
HSBC Multistrategy Arbitrage Fund (A sub-fund of the HSBC Alpha Trust Fund) (+)			2,000,000				*				—				—				35,623				—				(6)
Oak Hill Contingent Capital Fund Ltd.			10,000,000				*				45,000,000				2.05				979,622				—				Yan Vtorov Peter McHugh
Pimco Convertible Fund			—				—				750,000				*				13,358				—			Mark Hudoff
Ramius Fund III Ltd.			—				—				116,000				*				2,066				—				(25)
Wells Fargo & Company (26)			—				—				9,000,000				*				160,302				—				(5)

Revised Information Regarding Selling Securityholders

						Principal Amount of 2013						Number of Shares of
		Principal Amount of 2011				Notes Beneficially Owned						Common Stock
		Notes Beneficially Owned and				and Offered (USD) and				Number of Shares		Beneficially Owned		Natural Person(s)
Name of Selling		Offered (USD) and Percentage				Percentage of 2013 Notes				of Common Stock		after the Offering		with Voting or
Securityholder (1)		of 2011 Notes Outstanding (%)				Outstanding (%)				Offered (2) (3)		(4)		Investment Power
CODA Capital Management, LLC		545,000 (7)		*		-		-		9,707 (16)		-		Jerry O’Grady
CODA Capital ND Portfolio		395,000 (8)		*		-		-		7,035 (17)		-		Jerry O’Grady
Elizabeth D. Bruce Tr.		95,000 (9)		*		-		-		1,692 (18)		-		Jerry O’Grady
Gartmore Convertible Fund		1,495,000 (10)		*		-		-		26,628 (19)		-		Jerry O’Grady
James Mellor Trust		75,000 (11)		*		-		-		1,336 (20)		-		Jerry O’Grady
Lee David Invest. 2002, LP		70,000 (12)		*		-		-		1,247 (21)		-		Jerry O’Grady
Merrill Lynch, Pierce, Fenner & Smith(#)(27)		10,665,000		*		27,398,000(28)		1.25		677,952(29)		-		(5)
NMIC Gartmore CODA Convertible Portfolio		3,105,000 (13)		*		-		-		55,304 (22)		-		Jerry O’Grady
OB Pension — Gartmore		745,000 (14)		*		-		-		13,269 (23)		-		Jerry O’Grady
Richard Mueller		95,000 (15)		*		-		-		1,692 (24)		-		Jerry O’Grady

     Only selling securityholders that beneficially own the securities set forth opposite their respective names in the foregoing tables (including the tables included in the prospectus supplement and the supplements thereto) may sell such securities under the registration statement. Prior to any use of this supplement no. 3 in connection with an offering of the notes and/or the underlying common stock by any holder not identified above, the prospectus dated August 7, 2006 and prospectus supplement dated August 7, 2006 will be supplemented to set forth the name and other information about the selling securityholder intending to sell such notes and the underlying common stock.

     The prospectus supplement dated August 7, 2006 is also hereby amended by replacing the next-to-last paragraph appearing under the caption “Risk Factors—Risks Relating to Our Common Stock—Provisions in our articles of incorporation and bylaws, our shareholder rights agreement or Minnesota law might discourage, delay or prevent a change of control of our company or changes in our management, and, therefore, depress the trading price of our common stock,” as well as the paragraph appearing under the caption “Description of Capital Stock — Business Combinations and Control Share Acquisitions,” with the revised discussion of that subject appearing below.

The date of this supplement no. 3 is September 29, 2006