Do you have the Nvidia Control Panel installed as well? if so, is it version 6.03 (the latest one). If you do and you have an older version, I would suggest uninstalling it first, get the new version and install it before you install the drivers (this is based on another issue I am having with NVCP).
Ok, before you do anything, get yourself a copy of CCleaner or another good Registry Cleaner. Download it to a Temp folder or any other folder you can later find, run the installation and make sure you have an icon on the desktop or a way to find the app.
I was having issues with my drivers, the culprit turned out to be my monitor not having the proper x64 drivers installed but, this is how I installed my drivers from now on and I have had no problems whatsoever.
I unistall my current driver from Device Manager, I inmediately see the screen changing to regular vga drivers, it asks me to reinstall, I DO NOT do so, I know go to the Control Panel and uninstall the PhysX drivers as well (this is part of the 170/180 Nvidia series drivers), I Reboot now and Vista installs the std vga drivers, I then use CCcleaner to get rid of any instances or drivers remmants on my registry (when you open it, you'll see the registry icon, choose it and Run it. I reboot again for good measure.
Once I am back at the desktop, I go to the folder where I downloaded the drivers, uncompress the file directly to the same folder I saved it to, I again go to my device manager, go to my display adapters, double click on vga card and then, double click on driver tab and click on update drivers.
Once there, I tell it to let me choose the driver, click on "Have Disk", search for the folder where I uncompressed the executable and click on the .inf file, it starts doing the whole installatation process and tells me to reboot once its done.
I am sure there are other ways to do this faster but, so far, this has work for me in Vista x64... I wouldn't think it wouldn't hurt anything trying it this way.
If this fails, we will use the other method.