Vista 64 ultimate with dual NVidia 8400 GS, on 4 monitors, running non-SLI mode crashed when ever opening a PDF file.
Although the check from newer drivers indicated that the system already had the latest, I installed the latest drivers from NVidia website anyway. The driver installation package ran through without error, and requested a reboot. Curiously, Vista complained that the installation may not have been completed correctly. Ignoring the Vista warning message (what was I to do anyway?), I rebooted. After reboot I was able to open PDF file.
When I originally configured the system, I had attempted to operate my video in SLI mode. I could not get SLI to work with two cards/4 monitors. Ultimately, I configured in non-SLI mode. I now wonder, if trying out different configurations placed the video cards in an unstable configuration - which was cleared up when I reinstalled the drivers.