After a reply on anohter forum.....I've looked in the relevant section and on Page 42 in a little note at the bottom....Intel(R)QST....a small portion of system memory will be shared when Intel QST is enabled. That must be it
One thing that is annoying though is Note 2 on page 12 - To use a DDR II 800/667 memory module on the motherboard you must install an 800/1066 FSB processor. That explains why my RAM's only running at 533, the same as my Pentium D 805.