hi, this was really getting frustrating, i tried installing the drivers through Hardware Tools ad also tried Envyng but nothing was working ! finally i got the solution , manual labour is sometimes more fruitful! . I downloaded the driver .run file from the nvedia site, switched over to command mode ( Alt+Ctrl+F1 ) ,stopped the X server ,by writing :
sudo /etc/init.d/gdm stop and then installed the driver , after that i started the X server
and was at last successful
Hope this was useful!