Without saying which card it is this is, well, as useless as anything
we've come to expect from you.
ATI produce a *lot* of different cards. Some have excellent free support.
Some have medium-good and rapidly improving support. Some have rather
crappy support that will never improve (really old cards), or no useful
support at all, yet (really bleeding-edge ones).
Which it is depends on what card you've got (oh, and also what version of
the xf86-video-ati driver you've got.)