That should be ample for a 460 so long as it's a reliable brand or 80+ gold, silver or bronze.
I'm running a faster 5850 on a 550w with no problem, the recommended was 500, but I went one over.
For one, the GTX 460 requires one or two (I have no idea, I think it does not only depent on the chipset, but also on the manufacturer?) 6-pin connectors from the PSU, which I don't believe the current PSU in my system has, and:

Translation:
"Hello, is the PSU compatible with Palit Sonic GTX 460, seeing that it needs a 6-pin connector on the PSU?"
"The PSU is too weak to sustain this videocard, you'd need another PSU. Have a nice day!"
(That is a 1+2 sentences conversation I had with one of the workers that work at the online shop I bought the PC from, but he does not really know I already ordered it, actually.)