|Since you've tried different keyboards, that rules out any keyboard defects.|
If the problem still occurs when booting from a self contained OS, such as a DOS bootdisk or Knoppix CD, that would rule out virus entirely, and indicate bad hardware - most likely a bad keyboard controller, which may or may not be repairable
Hardware can't really be infected, and there's no 'payoff' to screwing up someone's keyboard - most modern trojans and virus are propagated for profit, and are intended to go unnoticed in order to accomplish their goals.
Sure - many things are possible, but it's not at all likely
... sorry for the delayed reply
I'm not one of those who think Bill Gates is the devil. I simply suspect that if Microsoft ever met up with the devil, it wouldn't need an interpreter