Running conflicting virus / spyware programs can often cause problems. But if your computer is more than a couple of years old, it might be a good idea to upgrade.

If you already have an installation disk for XP, you can buy a computer wherever, wipe it, and then reinstall the operating system from the disk. Otherwise, good luck! I don't think any of the big retailers sell computers without Vista anymore.

I'm curious to hear how the thing at Best Buy works out. You're right, it sounds very strange.