2.49 gig of ram out of 6.0 gig usable

Hello,

I have an Intel core i7 920, EVGA A1 X58 board, 2 GTX 285 SSCs SLI'd, 2 WD 10,000 RPM HDs set up in Raid 0, and a triple channel kit of DDR 3 (1333). I'm running an upgraded version of Windows 7 Ulitimate (64 bit).

My system recognizes all 6 gigs of ram but only 2.49 is usable. How do I increase my usable physical memory????