Wolf_Racer,
I too had problems getting a graphical login when I installed 10.0 RC1 with the i810 chipset. "Startx" gave me the same exact error:
GartInit: Unable to open /dev/agpgart (no such file or directory)
I810(0) AGP GART support not available.
As root, type "modprobe intel-agp" (without the quotes) and then add "intel-agp" (without the quotes) to your /etc/modprobe.preload file and reboot. It should work now ;)