8800gt shared memory?

[hybrid-kernel]

Several days ago I got an 8800gt, and I am very glad I did. My only problem is that after inserting it, my available ram went down from 3.8gb (4-128mb onboard) to 3.5gb (card is 512mb). It seems that it is not onboard graphics thats doing this as it got disabled automatically once I inserted 8800gt. Now before you tell me that there's the x86 os limitation, let me tell you this: I use linux, not windows; I use x64 not x86; this is not an os issue as it says in bios that only 3.5gb of 4 are available so it doesnt matter what os I use.

Any help would be nice as I'd like my ram back.

mobo: asus m2a-vm
cpu: amd athlon 64 x2 4200+ (@2.6ghz)
mem: 4x 1gb (2 kingston; 2 cruicial) dual-channel