The requirements for running vista are pretty low. It can be done on a 1Ghz cpu w/ 512MB of RAM. It will run like crap, but it can be done.
A simple search of ebay will bring up all kinds of cd-roms. I've personally purchased a few lots of them.
Anyways, like I said, it's a good idea to rule out the simple things. Specially when there isn't much that will cause this type of problem.