You found what I was looking for...
Well... your chipset seems not to be properly supported... so... you can try to update the kernel and the modules of your distro and expect your chipset to be supported. For instance try to go up to 2.4.21 or 2.4.22 kernel and modules...
The cheap fix would be to follow the log file advise... so try this:
#insmod agpgart agp_try_unsupported=1
#modprobe nvidia
#startx
Check out the dmesg output after that, if it still does not work.