Keyboard loggers and a lot of spyware could caus the cursor or window focus to change. Or you inadvertantly enabled the voice command/input in XP and its working.
Read your post. The lack of details make this a first cut and possibly bad guess. You could be connecting from some 1985 Macintosh via a modem and its finally failing.
I have what seems to be a pulse, that goes through my computer every few minutes. If I am typing, I loose the prompt. I have to go back and establish the prompt again to continue typing. When playing a game, I'm knocked out of the program back to windows and I have click on the task bar to go back to the game,which went to pause. None of my other electronics are affected,so I guess a power surge is out? Please help, this is driving me nuts. Thank You in advance. Bill