...from: http://www.apple.com/macosx/uptodate/

Customers who purchase a qualifying new Macintosh computer on or after April 12th, 2005 that does not have Mac OS X v10.4 "Tiger" included can upgrade to Tiger at a cost of US$9.95.

The program ends on July 22nd 2005. Your order must be postmarked or faxed by July 9th 2005, so order your upgrade now.

The list of qualifying computers can be found at: http://www.apple.com/macosx/uptodate/list.html