If you can see the system on the screen, you probably don't need any more drivers but if you look in Control Panel>System>Hardware>Device Manager and right click the Display Adapter, you can then right click whichever adapters are in the list. Find the Properties and click Driver then Driver Update and let it roam the Net for the right one. If you can't find one that way, click on Details then scroll to HardwareIDs and take a note of the four characters which follow VEN for Vendor and also the four following DEV for Device.
Go to http://www.pcidatabase.com and input those characters in the two relevant boxes and follow the trail to the right driver. When you find the list of the Vendor's drivers, they aren't in order so use your browser's Find facility to track the Device details. With luck you'll have an executable file but some will be a zipped folder.