That crappy PSU should be fine with at GTS450, but I wouldn't trust it with a GTX460. Now you may be able to run your PC and a GTX460 just fine on that PSU, but personally I wouldn't chance it. Read up on PSU tiers herehttp://www.eggxpert.com/forums/thread/323050.aspx
If you want something to last you a while and perhaps allow you to SLI down the road get at least a tier 3 unit. If you just want a decent budget PSU for now go with a tier 4, but for the love of fluffy bunnies don't go with a tier 5 PSU or anything that's not even on the list!!!!!!!!!