Quentin try this download driver cleaner pro from (
http://downloads.guru3d.com/download.php?det=745 ) and the latest drivers from Nvidia.Follow these steps
1. Uninstall nvidia drivers
2. Boot into safemode with internet and anti-virus off
3. Run driver cleaner pro to remove excess nvidia drivers
4.reboot and install new drivers.
The reason you are turning off the internet is because Vista tries to install a generic driver which interfers with the Nvidia drivers. This info was given to me by a tech at SLi forums and worked on my Pc. Good luck.