What is the exact error that you get if the nv driver is replaced by the nvidia driver in your xorg.conf? i.e.
Code:
Section "Device"
Identifier "Gforce 7800GT"
Driver "nv"
BusID "PCI:1:0:0"
EndSection
becomes
Code:
Section "Device"
Identifier "Gforce 7800GT"
Driver "nvidia"
BusID "PCI:1:0:0"
EndSection