I have an ATI card on arch too. Radeon X1400 (my laptop is ~2 1/2 years old too). I haven't had any real 'problems' with it.... but I also don't play many games. Wesnoth and starcraft work, and in general that's good enough for me.
Anything 3d is noticeably worse.... for instance, I can't get Oblivion to play. It plays a few frames, freezes, plays a few frames, freezes, etc. The reason is mostly just because ATI doesn't care about their open-source drivers. They're developing far slower than the windows ones (and support may have even been dropped altogether now?), and the open-source drivers can't match ATI's windows drivers in power... at least yet. Needless to say, if I'm going to continue using linux on my next computer (which I almost certainly will), I'm getting an nvidia chip.
Are you sure it's your graphics card that doesn't work, and not something else? I don't have any problem with gui's at all.... it's just the 3d support that makes certain games kind of rough.
Archwiki is a fantastic resource... though I'm sure you've already found it, if you managed to install the system. I just use the open-source driver, and it works perfectly fine.... there's a whole page on installing it
here.