I would think that you should be fine. Here is the requirements posted on eVga's website for their 8800gt 512mb:
Requirements
Minimum of a 400 Watt power supply.
(Minimum recommended power supply with +12 Volt current rating of 22 Amp Amps.)
Minimum 450 Watt for SLI mode system.
(Minimum recommended power supply with +12 Volt current rating of 24 Amp Amps.)
An available 6 pin PCI-E power connector (hard drive power dongle to PCI-E 6 pin adapter included with card)
Your PSU, if I read it right, should be at 26A on the 12V rail, so you should be fine. Now you might want to consider how old your PSU is, because all PSU's loose capacity over time. So if you load up your PSU too much, you might run into problems. IMHO I think you should be fine. If you start to do some OC'ing than I might consider getting a newer PSU, like the Antec EW 430w one at the minimum, which has 30A on the 12V rails and is $70 right now at newegg w/a $30 MIR, so you could have one for $40!! Not a bad deal at all. If you want to future proof your PSU, I'd go with at least a Corsair hx520w PSU or a Antec 550w Neo or maybe a PCP&P 610w Silencer. The Corsair is about $110, Antec 550w Neo is about $100, and the PCP&P 610w is about $130.