I have tried the one packaged with Ubuntu, and then downloaded the one from amd.com and still have this issue. It's not a "huge" issue, but it's in regards to 3-D gaming. The issue is that there seems to be a consistent "start & stop" behavior that happens randomly while doing some of the following things.

1) Playing World of Warcraft w/ Wine
2) Playing Nintendo 64 games with Mupen64

Both of these activites run pretty good, but it's like, it'll run fine for 5 seconds, and then it's like it'll skip when it drops a frame instead of transitioning to the next frame smoothly. It's like millisecond pause that randomly happens when doing these two things. I haven't yet tried any 3-D Linux games like Nexuiz, but I'm wondering if this is an issue with the ATI driver or with Xorg or what? This card has 256MB of video memory, and all these things worked fine in Windows (the machine shipped with Vista), now I'm not comparing this to Windows necessarily, I'm just noting that the video card is more than capable, so the issue is obviously software related.

Edit: I am using the Linux version of Mupen64.

Hmm, I have gotten this type of "five second frame drop" behaviour with XMAME as well.

I suspect that your system is going "elsewhere" i. e. some kind of interrupt occurrs that forces processing to go to another thread or process, and the game thread then lags.

I only get this type of problem when my system is loaded (load avg. above 1.5) AND I try to play a MAME game at the same time.

I think you can try two things:

1. Prioritizing the process

Try renicing the game process to the lowest priority number you can.

2. Unloading your system

Kill unneccessary applications or background processes to free up more CPU power for gaming.

Hope this helps...

I've discovered the issue with the N64 games was just that I was using bad plugins in Mupen64. I downloaded Mupen64Plus for AMD64 and it works flawlessly, even better than Project64 did in Windows(a few graphical glitches aren't present that were there in Windows), so that's cool. Still trying to figure out how best to remedy the issue with WoW jumping a little, it automatically starts with a nice level of 0, and won't let me set it any higher(lower than 0).