Assuming you have now made progress in getting the correct resolution for your display and are still using the “unichrome” driver to support your VIA K8M800 chipset, to check/troubleshoot 3D support please post results of following commands (terminal as normal user):
dmesg | grep -e agp -e drm
grep rendering /var/log/Xorg.0.log
grep "(EE)" /var/log/Xorg.0.log
grep "(WW)" /var/log/Xorg.0.log
Also, run glxinfo in terminal (normal user). In first few lines of output, it should report “direct rendering: Yes”.
Run glxgears in terminal (normal user). Post the approximate steady-state FPS reported, and any issues observed with the rendering of the gears, or failure.