It's also worth noting that there are a fair number of people (at least I know some) who use their old XP licenses for testing Windows software in VMs, especially if they're usually working in Linux or Mac OS X.
Do you, yourself do this?
I used to do that, but nowadays use the VMs Microsoft provides for testing webpages under IE [1] and multiple windows environments. Just download your favorite flavor and run. I'm not sure about limitations they might have, but I was able to install other software just fine.