I've same problem too
I've the same problem with the same videocard (Gainward TI 4200) but under RH 9 (Shrike). After installing the driver a blank sreen appears (or sometimes a black screen with some random chars). This is because the X-server crashes invact if U press ctrl-alt-canc the system restart, but the ctrl-alt-backspace doesn't function. The problem is that the debug info in XFree86 doesn't report EE or significant warning.
Now I'm going to post a my own thread stressing the problem I hope to solve it asa soon as possible.
Have U solved the problem?
P.S.: if u change in XF86config nvidia to nv you don't use the nvidia accelerated driver but the generic for Geffo 4, that driver works fine also to me (and I haven't still uninstalled the accelerated one)