In the case of Dell, any dell Windows XP install disk will install on a dell machine. There is some sort of BIOS verification. (This is purely anecdotal but I’ve not be let down yet)

I wouldn’t advise trying to “clean” a serious infestation, so I think you are on the right track.

If it’s your own computer you should have kept the install media. If you are actually going to a repair shop then they will tell you how they are going to handle it. You wouldn’t need a new disk for every repair though – just one disk once.