Further to what signals said, I have an ATI card in my system (I'm running XP Pro, which is close enough that the problems will be similar).
ATI makes great hardware, and L O U S Y software.
When you first got the card, and loaded the software, I imagine Catalyst, the ATI Media Centre, a video file player, and a DVD player loaded as well as the card's drivers.
I had no end of problems with my system and Fab with all that loaded. The only solution I found that worked was to dump all the software except for the card's actual drivers, and all my problems disappeared.
There are conflicts with some of the drivers for the DVD player and file player that cause Fab to behave very erratically.
Try that and see if things behave better afterwards.