I believe that AGP cards are almost out of production. If the card was old, it may not have a driver, but for WinME I don't know. I have found that drivers, codecs, and whatnot, it is easiest to open your own folders for keeping track of them, and collecting them. Many different media players use different ones for different media. That is that one pack or driver won't work for every type of media, even though they can be written that way.
If your onboard video is bad, I dont think you'd get anything, so even if the AGP card doesn't work (worst case), then I would suggest you get a PCI vid card instead, that matches the PCI slot in your motherboard. At worst you'd be out $30-40