Im getting the same prob with mine.. im no expert really but my mother board (KA92 Platinum for AM2+) is reading the memory sticks as 800Mhz!
I feel ripped off.. it really says 1066Mhz on the case..
They occupy 2 slots only on my mother board and I still have 2 more available..
I am also running on a windows xp 64 bit OS.. and it reads 4 GBs which is good i guess..
any other ideas and suggestions?