The easiest way to tell what version of X you're running is to "head" the log file:
# head /var/log/Xorg.0.log
if you're using X.org or if you're using XFree86:
# head /var/log/XFree86.0.log
Here's a short explanation of the differences between Xorg and XFree86 posted a few years ago if you're interested:
Difference in Xorg & XFree86
As far as the ATI driver stuff, I don't have much experience (as I use NVIDIA). But NVIDIA definately has better Linux support than ATI. Here's a quote from a recent article in TomsHardware.com:
"In the case of NVIDIA, for example, its Linux driver developers are among about 400 of the company's total software engineers. They are busy in their development labs programming in C and C++, and working in conjunction with the QA department group that tests the drivers...Meanwhile, for ATi, Linux remains largely a minority segment."
-- Graphics Card Drivers Can Make The Difference
If you need help with installing the drivers, maybe you could be more specific as to what's wrong.
-- the dudeman
PS Here's the beginning of the article, if you're interested.
Does Linux Have Game?