Is an Intel core 2 quad q6600 processor compatible with an asus p5gd-vm motherboard?

No. The ASUS P5GD1-VM motherboard uses an Intel 915 chipset, which is too old for a Core 2 Quad (or even a Core 2 Duo). Probably the best processor you could get running on that board would be a Pentium Extreme Edition 840.