I've had several ATI cards and never had this problem :shrug:
All that doesn't change the fact that removing their drivers is a pain in the ass, and you have to use 3rd party programs (drivercleaner pro, driversweeper etc.) in order to remove them completely. Installing new drivers won't help until you've removed every last trace of an ATI driver from your computer. The ATI Catalyst Install Manager just doesn't do what it's supposed to.You can't install ATI Drivers on a mobility chip without using Mobility Modder. Go here, use this app, then you can install the latest drivers.
ATI MobilityModder - DriverHeaven.net
Been there, done that, it's not ATI's fault, they just don't support every chip put in every laptop, they have those companies support them.