How can I set the VGA on my dell inspiron 1720 back to normal after windows reinstallation?

I re-installed windows vista on my dell and i installed the drivers, however I'm supposed to have nvidia geforce 8600gt which was working fine until i made the reinstallation. Now it just says I have standard vga graphics adapter and i can't install any nvidia drivers. What is wrong? Please help!How can I set the VGA on my dell inspiron 1720 back to normal after windows reinstallation?Try windows update or get the driver file from dell for the video. What do you mean by 'can't install'? As in the system won't let you?