[Pc_Support] CompUSA has Windows XP SP2 Upgrade on-sale for $99 - $50 rebate ...

[Bryan J. Smith]

If you need a copy of Windows XP, the upgrade version is on-sale for
$99 - $50 rebate at CompUSA.  The rebate is with CompUSA, not
Microsoft.

http://www.compusa.com/products/product_info.asp?product_code=314685

Even if you don't have Windows 95, 98 or ME on your system, all you
need is one of the aforementioned installation CDs to install.  I.e.,
it's basically the same as the OEM or full retail, non-upgrade
versions, except the part where you have to stick in the Windows 95,
98, ME CD into the drive during the install process to verify you're
upgrading.