I purchased my macbook before Leopard was released and I came across this link, so I wanted to share it just in case there were people like me who wasn't aware of this!Hardware Up-To-Date
Customers who purchase a qualifying new Macintosh computer or an Apple Certified Refurbished computer from the Apple Online Store on or after October 1, 2007 that does not have Mac OS X v10.5 Leopard included can upgrade to Leopard.
If you purchased your system directly from the Apple Online Store, follow one of these links to participate in the program. Subject to terms and conditions.
here's the link: http://www.apple.com/macosx/uptodate/