The Geforce cards have special closed source drivers, available from www.nvidia.com
without them i *think* the card will only run on XFree86 3 not 4.
I had to sort all that out at the start of the week, all sorted out lovely. Mandrake didn't install X windows 4 completely, and i found out that i was using 3 without knowing. the only real way i know of to find out quite which server you are using is to run 'ls -l /etc/X11/X'.
If this points to /usr/X11R6/bin/XFree86 it should be 4, if it's /usr/X11R6/bin/XFree86_SVGA or similar, it'll be 3 i THINK.
make sure all the 4.0.3 rpm's are installed from your system, and remove all 3.3.6 ones (except Xfree86-contribs) using rpm -e. Probably easiest to remove the old ones once X is working.
Oh and another thing, to try and make X use 4.0.3 run 'Xconfigurator --expert' and you SHOULD be able to choose which version...
Oh, and you should only ever need to run startx to load it, not startkde or such