True, that's ~ how much the card uses. But that's cutting it close. Usually the minimum recommended is 17A on the +12 rail.
@OP: Mind listing the exact PSU you have?
By his own admission he's got four 18 amp rails, and with the PEG connector generally on it's own rail, power isn't the likely cause of the problem.
I always like to keep invisik
in mind, he's the forum member running dual GTX260's (11 amps consumption per card ) on a Antec EA500 with it's dual 17 amp rails.