That's actually strange. It should still detect a PCI card and at least read the vendor ID and Device ID even if it doesn't load any drivers. Do you have any other PCI cards you could slot in? I am wondering if your logic board has issues.
Not sure if I have any other Mac-compatible PCI cards... And regarding the logic board, yes, it does seem one of the three RAM slots doesn't work. But when I checked the diagnostics in the System Profiler, it only mentioned the failed RAM slot, nothing regarding PCI. Hmm...
And it does feel like it's in all the way, too.