I have recently built P5WD2 Premium and I needed to flash BIOS for dual core suport. (F arkin Pain)
The second Asus MB I built P5N32 SLI Delux (intel version of A8N SLI) needed a revised BIOS update for Dual core suport (It had a red sticker on the retail box that said it would suport dual core). Otherwise I would have to flash this MBs BIOS too!
ASUS tech suport is USELESS in my opnion (from recent experience)
From my experince I think ASUS rushed out a lot of their MBs with incomplete/old BIOSs that basically dont suport anythink with dual core writtin on it.
I would not be suprised if you needed to flash BIOS for your MB aswell... Good luck finding an old CPU to flash your BIOS and havefun with that tube of thermal paste.