Just to help clear up any confusion, ATI's proprietary drivers are generally called
fglrx and there are a couple of open source ones that ship with Xorg,
radeon generally being the one you would want to use from among those. These drivers are almost certainly kernel modules, and so you can check which one is loaded with:
Code:
lsmod | egrep 'radeon|fglrx'
(More refined methods exist on various distributions, but the above should work just about anywhere.)
Also, you may want to look at the output of
glxinfo, specifically the vendor strings. If you see Mesa in one of them, then there is a chance (though not a guarantee) that software rendering may be being performed.
As part of the troubleshooting process, I would definitely start by stripping down the in-game rendering options as much as possible, and then adding them back one by one or cranking them up in increments. It could be that a particular option, such as grass, is the killer.