I'm having the same problem with ubuntu 9.10, but with an NVIDIA card, Bioshock works great but Guildwars and Sims3 both fail. Did you use PlayOnLinux to install your games? Other than that the only advice I have atm is to make sure you edited your x11 conf file (if that is necessary for ATI drivers) because I know nvidia drivers need a setting changed from "nv" to "nvidia" to use the official drivers instead of the ubuntu or kubuntu drivers.
