i have this PSU http://www.arktechinc.com/acbel470/pc7004.htm
with 2 12+ (18 AMP)rails but not sure if it is sufficient for the HD 3870 X2
if not any suggestion for a cheap PSU
i have GA-690G-S3Hmobo ,AMD 5600+ CPU ,2 320gig hdd,1dvd BURNER,2GIG G-SKILL RAM
That is 312w/12v = 26A, so I'd probably say no way. An 8800gtx consumes about 132w by itself and a 3870x2 consumes about 188w peak. So I'd be betting that you'd need about a 35A on the 12V rail to support the 3870x2. Plus you'll need an 8 pin and 6 pin PCI-e power connection to take full advantage of the card, which I don't think that PSU has those connectors.