Repairing your XP installation wont harm anything. Again, as member suggested, if you were on an operating system that is not Windows then viruses are really nothing to worry about. The most family friendly is probably OS X and if you want to get a little more technical then try using Ubuntu like I do. Takes a little bit of nerdy-know-how and quite a bit of Google at time to get it working exactly as you want it but it saves the worry about viruses and such.
Oh and as Kiah said, you'd be laughed out of the world if it was something like a CD or floppy left in the drive that caused the problem.
Seems as though everything I would have said has been already done.
25/08/2007
pinked - Kiama, NSW