is this enough for the 3870 x2

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.