press Ctrl+Alt+F1 to switch to a virtual console. Or start your system in single user mode. Use google to figure out how to do this if you don't know.
login with root priveleges and start editing /etc/X11/xorg.conf in your favorite text editor. Make a backup first and copy the backup somewhere else so that it is not accidentally overwritten!
Find Section "Device"
Under that change Driver to "vesa"
Save file and press Ctrl+Alt+F7 to go to login screen. Wait for about 10 seconds and press Ctrl+Alt+BackSpace to restart X. You should now have a login screen. Expect the resolution to be terrible, but you can atleast login and get a gui desktop.
You still need to install nvidia's drivers.
I am using Ubuntu 7.10 on my laptop with FX 570M and it works well. I generally use the 'envy' tool
but as far as I know, it is available only for debian and ubuntu.