First of all, when you update your drivers, you do not have to touch anything in the registry. The exact process you need to go through to update drivers is different based upon how the drivers were packaged on the net.
If your driver file came as a self-extracting executable, then all you need to do is run that file; the update should occur automatically. If, however, the download consisted on a ".inf" file and some ".dll" files, you'll need to update the driver manually. To do this, go to Control Panel and select the System icon. Go to the Device Manager, and select your video cards and look at its properties. From there, select "update driver". When the next window appears, select the location where you saved the ".inf" file you downloaded. After this, the install should proceed without incident.
If you want to play it safe, you should uninstall your current drivers before installing new ones. Of course, that's up to you; you should be able to update the drivers without first removing your current ones, it's just that there may be conflicts down the road, which could lead to a whole other mess of problems.