Ram quota not adding up

Ok i just got a new 3.Ghz machine
Just yesterday i upgraded from the standard 512 stick of ram and got another 512 stick of ram

but i had this problem and i thought it was just nothing until now that i have all this ram i can see that its really weird

im operating on 2000 and when i look at the task manager, the ram usuage is ALWAYS above 400 mostly around 600. But when i look at the running processes, i cant seem to add up to more than about 100, and thats really pushing it. Even with no programs open and most things shut down except maybe virus scan its above 400.

Where is all this phantom ram usage comming from? I’m contimplating getting a 1gb stick, when i play games it still gets over a gigabyte of usage

CPU usuage is always steady and reliable. stays under 20%, and mostly fluctuates between 0 and 10%, even under load