Asus p5w64 pro & Corsair xms2 compatibility issues

Hi,
Finished building my pc about a month ago, but im baffled on how to make my memory run at pc2-6400 mode.

My bios post message reveals that im running at "pc2-5300 single channel mode."

I have an asus p5w64 pro, & checked what memory can be run in 6400 mode according to my MB manual.

the memory i have purchased is Corsair 1GB DDR2-6400, which should work according o the manual's qualified vendor list for 6400 compatible memory.

quote from manual:
SIZE VENDOR CHIP No. SIDE(s) PART No.
1024mb Corsair Heat-Sink package SS CM2X1024-6400C4


My full system specs are:
Pentium D 945
P5w64 pro MB
WD Caviar 160gb
Corsair XMS2 DDR2 1gb
nvidia 7900GS 512mb
Soundblaster audigy SE
Sony DVD-RW

Any help or info appreciated.

Darren