Keep old mobo?
 

I think I am going to up grade

Legend: [Old --> New]

Motherboard:Asus P5W DH Deluxe --->Asus Striker Extreme

Video card: 7900 GT OCx2 [Can't use the second one... since its only crossfire...]--> GeForce 8800 GTS OC / 320MB GDDR3

RAM --> OCZ Reaper HPC Edition 2GB PC2-6400 800MHz

Should I get motherboard or buy the video card?

If you want to run DX 10 games, I would go for the Geforce 8800 GTS (1st generation), and that would mean you would have to be running Windows Vista. I'm positive 7900GT does not support DX 10. But if you don't care about DX 10,and just care for a speed increase, go for the motherboard(cheaper option and does it supports the second card?). The increase from the second card, I THINK, will give around a 10-30% performance increase.