I wouldn't exactly recommend running it on that. My buddy runs it on a Corsair CX500, but that is actually a good power supply. The card requires 2 6-pin connectors. I don't feel that your power supply has the proper amperage to support the 6870.
If you want to do step by step, go for the power supply first, then you wont have to worry.
Theoretically you are getting 30A on the +12v rails but that PSU looks suspect and probably doesn't deliver that kind of constant power to the rails, I personally wouldn't try. I would first thing upgrade your PSU as its the only component that can survive 2-3 upgrades and is the most fundamental part of a setup. A good PSU sets you for a long time.
thank you for your reply guys, i appreciate it
- if i'm getting 30A on the +12v rails, will that be enough ? what do i do to know it really does what it says ?
- what about ATI HD6850 , is there a big difference compared to the 6870 ?