I actually do have more than a few pcs but I use they each serve a different purpose and a few of them are multi-boots. If the purpose that I'm doing for a specific install for is general enough, I could install any version of any of the OSs (XP, Vista and now 7).
For example, the computer I use for "general" computing was Vista Home Premium x86, up to few days ago, until I clean installed 7 Ultimate x86. Another computer, I use for "development" which is a quad-boot, Vista Home Basic, XP Professional, Vista Business and 7 Professional (all x64).
That's five on two computers.
...and I have more.