If you think you might need a Windows 7 upgrade and you live in the U.S. or Canada I have a low-risk deal for you. Through Saturday, July 11th you can get up to 50% off on your Windows 7 upgrade. I would pre-order through Amazon (affiliate) so that you can get in on the deal. Then if you change your mind or you see a better deal before Windows 7 ships (October 22nd) you can always cancel the order. After July 11th it reportedly goes up to full price so don't wait.
Amazon U.S. Windows 7 Upgrade Pricing (50% Off Preorder):
Rumors of "Family Pricing" could mean you could get a better deal if you need multiple upgrades, but as I said you can always cancel your pre-order once those details surface.
Upgrading from Windows XP?
Oh, by the way I read yesterday at Maximum PC that if you're upgrading from Windows XP like I will be on one machine - remember that you have to do a clean install. In other words you can't take all of your settings and installed programs and "upgrade" that information into Windows 7. You basically start from scratch and will need to reinstall all programs and re-set settings. Honestly this isn't a terrible thing as this is something I would recommend on a new OS install/upgrade anyway, but definitely something to keep in mind.