Little Graphics problem

I have went into the bios of my new hp desktop, and I have changed the graphics output to the pci express

Yesterday I installed an nvidia 7600 gs 256. I quess the pci express card before mine is dumb or something, but it must have been sucking out memory from the computer.  Here is my real real problem

NVIDIA System Information report created on: 03/19/2007 14:22:17
System name: HP

[Display]
Processor:  Intel(R) Core(TM)2 CPU          4300  @ 1.80GHz (1800 MHz)
Operating System: Microsoft Windows Vista
DirectX version: 10.0
GPU processor:  GeForce 7600 GS
ForceWare version: 100.65
Total available graphics memory: 751 MB
Dedicated video memory: 256 MB
System video memory: 0 MB
Shared system memory: 495 MB
Video BIOS version: 5.73.22.50.56
IRQ:   5
Bus:   PCI Express x16

Why is 495 mb of system memory being shared for the total graphics memory?

Please someone tell me how to turn this off please please please

ok

thx