MTK358, he did say "when I use the default it works fine". The default one would be the open source -ati driver.
andrew2325, I've used a HD4350 with the catalyst drivers Ubuntu packaged for 9.10 but, of course, each users success is going to vary depending on the exactly hardware in their machine. If you can't get the catalyst drivers working, you could try using an updated version of the open source drivers which do support 3D acceleration. You could install it using the xorg-edgers PPA:
It would also require a newer kernel, which I believe you can get from the kernel PPA:
Unfortunately, I have no experience with either of these, so I wouldn't really be able to assist if you ran into problems.