Being a techie I find that a lot of my friends are more than willing to unload their old PC's on me.  Normally thats all I get, the pc; no documentation. Which means I have a helluva time trying to identifying the components and find drivers for them.  Here are some sites I find absolutely essential to doing so:

DriverGuide.com and WinDrivers.com are simple straight forward databases of drivers for known devices.  MoboCop, however, will help you determine what kind of motherboard you are dealing with so that you can go ahead and find drivers for it.