I've got a ATI Mobility M9 Radeon 9000 card. I searched
www.ati.com for drivers, but they only offer drivers for Microsoft Windows. But as I mentioned in my first post, redhat recognises my ATI card, so doesn't that mean that the drivers are installed correctly?
Another thing I just remembered: Redhat says that my monitor model is unknown. During installation I just selected the Generic Laptop Display (or something like that) with the correct resolution (1400x1050).