Depending on model, you will be using either Intel graphics or nVidia.
Intel(R) 82915G Express Chipset Family
Intel(R) 82945G Express Chipset Family
Intel(R) Q965/Q963 Express Chipset Family
or
NVIDIA GeForce 8400 GS
NVIDIA Quadro NVS 285 PCI-E Series
NVIDIA Quadro NVS 290
NVIDIA Quadro NVS 55/280 PCI