is your card a PCI-E 2.1? your athlon IIx2 mobo is probably PCI 2.0 and your athlon's is probably 1.0. PC makers like DELL, HP, Acer, etc., tend not to have a BIOS that supports 2.1 cards on 1.0 x16 slots.
Yeah, its a 2.1 card, I also looked at my motherboard on the HP website, and there was drivers for the BIOS, but only for XP. But, If i was running XP and installed it, I'm not sure it would solve the problem.