I had the same problem after choosing to to the 3D acceleration option when installing LE2005 edition. I'm havn't noticed anything beng really slow while using linux/KDE. It does take awhile to boot(a fair amount longer than windows does) but I've read stuff where linux can take awhile to get going. I havn't given a try to installing ATI drivers myself as its not exactly a user friendly experience. I guess Nvidia is easier to get up and running. I'm not really interested in trying to run games or anything under linux so guess I've been happy to just leave it as is for now, and not do something that could mess my whole system up.
I'd be interested in anybody who knows how to make is so the ATi driver doesn't even attempt to start at least so I don't have that happening.