Memory being hogged

I just built a new system:

eVga A1 680i
e6300 Core 2 Duo 1.83GHz
320MB 8800GTS
2x512MB Patriot Dual Channel DDR800 with heat spreaders

My problem is even with nothing running at all with about 19 processes, only 60-70% of the RAM is available. With Firefox and MSN (sometimes on call) open it's usually between 60% and 70%...I'm confused, and as some reviews on the site I bought it from (newegg) I may have to change the voltage and/or timings. I'm wondering why in the world it would do that though, I know it's compatible with the motherboard, I can play Dark Messiah on all the highest settings just fine, but when I'm on the loading screens it either crashes when it's 75% loaded or BSODs out. I don't have great cooling so I'm thinking the graphics card could be overheating...but it was off all night and when I played it in the morning it crashed the game (instead of BSOD after hours of gaming)

I ran memtest86+ for a while everything's fine there, otherwise. Thank you, I appreciate any help!

Thanks for the quick reply, love foxes btw.

Windows XP SP2, and there is literally nothing else going, nvidia control panel, but disabling it doesn't change anything. TweakRAM tells me the steady 39% it's at now (which is as always) is being used for Swap File Usage?