How to determine what driver is needed for an "Unknown Base System Device" in Device Manager

Sure.  Start - programs - accessories - system tools - system information.  Click on "components" and then expand "problem devices".  This will identify your devices.  Look at the PNP Device ID line of each entry.  Note down the VEN/DEV numbers (4 digits long) and look them up here:

www.pcidatabase.com

Look for drivers for the identified chips at the manufacturer's website.

Try the Unknown Device Identifier tool here: http://www.freewindows.dk/fw/modules/mydownloads/viewcat.php?cid=145&min=20&orderby=titleA&show=10

You have this problem because you downgraded from Vista to XP?  If this is so you can take comfort in knowing that you are not alone.  Fortunately, one kind soul has gone to the trouble of creating a set of instructions in excruciating detail specifically aimed at your computer.

http://forum.notebookreview.com/showthread.php?t=188992

"Unknown System Based Device" sounds like a chipset identification problem, try installing the latest chipset driver for your OS.

The suggestion from "ts iap" worked for me. Thanks.