Try manually uninstalling the driver by using the following procedure:
1. Control Panel=>Windows Update=>Change Settings=>"Download updates but let me choose whether to install them".
2. Download the latest driver from the nvidia website. Drivers - Download NVIDIA Drivers
3. Go to Device Manager, select your display adaptor, and uninstall it, choose to also delete drivers when prompted.
4. Reboot computer into safe mode by pressing f8 when the computer boots, when prompted to install new display driver choose "never install a driver for this device"
5. Navigate to c:\windows\system32\drivers\ and rename the file nvlddmkm.sys to nvlddmkm_old.sys. Take note of the date of this file
6. Navigate to c:\windows\system32 and rename any other file of the same date as nvlddmkm.sys which begins with the letters 'nv'
**ADDED FOR CLARITY***
nvcplui.exe become nvcplui_old.exe
nvd3dumx.dll becomes nvd3dumx_old.exe
etc..etc..etc..Repeat for all files with the same date as the file you found in step 5, they begin with the letters 'nv'
If it is too tedious to rename all the files, you can simply delete them, or move them to a different folder.
6a. For 64bit Vista, repeat step 6 in c:\windows\sysWOW64
7. Reboot to normal Windows, if prompted again to install a driver choose "never install a driver for this device.
8. Install the driver which you downloaded from the nvidia website.