Upgrade and New PC

Hi i want to upgrade my current pc video card and then transfer it to my new pc when i have the money.

- I am not going to overclock on either

my current pc specs are

inter core 2 duo e6850
8600gt GPU
2gb ddr2 RAM
4core1333-fullHD Motherboard
OS Vista 64bit
PSU 400w

I am going to get a 850W PSU for my new PC and a GTX 580. i can afford that now so could i add this to current pc and then add it to new pc later?

And these are the things im getting for new pc

MSI P67A-GD53 (B3) Intel P67 Express Socket 1155 Motherboard OC Genie II
http://www.scan.co.uk/products/msi-p67a-gd53-%28b3%29-i...

Intel CPU Core i5 2500 Sandy Bridge Quad Core Processor
http://www.scan.co.uk/products/intel-core-i5-2500-s1155...

MSI 1536MB GeForce GTX 580 Twin Frozr II/OC NVIDIA Graphics Card
http://www.scan.co.uk/products/1536mb-msi-gtx-580-twin-...

Fractal Design Core 3000 ATX Case
http://www.scan.co.uk/products/fractal-design-core-3000...

Corsair Memory Vengeance Black 8GB DDR3 1600 MHz CAS 9 XMP Dual Channel Desktop
http://www.scan.co.uk/products/8gb-%282x4gb%29-corsair-...

Corsair Enthusiast Series TX850M Modular, 80 PLUS Bronze, 85% Eff', SLI/CrossFire, EPS 12V
http://www.scan.co.uk/products/850w-psu-corsair-enthusi...

+ 1TB HDD
+ 70GB SSD
+ DVD Drive
+ Windows 7 64bit