Post the output of the command 'glxinfo'. This verifies whether openGL is actually loaded and available with acceleration.
Have you added the 800x600 resolution to your config in /etc/X11/XF86Config? If you could post this file, and the /var/log/XFree86.0.log, the problem might be shown in them. You can attach these files to the post, better than pasting them in.
"..the triumph of evil is for good men to do nothing."
VIDIA video driver RPMs for Fedora
:: see yum repo at livna.org