What's the exact model and manufacturer of the controller card? I'm checking out Western Digital's website right now, but they don't list any controller cards made by them. The one that looks closest is the SIIG. Is that it? It's a 2 channel SATA RAID controller card.
What does Windows identify it as?
The card could be bad, but let's try a few more things before returning it.
EDIT: Signed or not signed, the drivers should work. Also, not being on the HCL just means they didn't submit it to MS for testing. There's plenty of hardware not on that list that works perfectly with XP.