You should be able to "roll back" the driver to the one you had previously, like this:
1. Control Panel (classic view)->System
2. Click 'Hardware' tab, then 'Device Manager'
3. Find the video controller entry directly under 'Display adapters" and double-click it.
4. Click the 'Driver' tab and you should see a button labelled "Roll Back Driver". Click it.
If that doesn't work you could try 'System Restore', though I must confess here that I don't know if that option will "roll back" or restore a third-party device driver. Start>All Programs>Accessories>System Tools>System Restore. It presents you with an on-screen calendar. Choose a date just before you installed the driver update.