before investing in trying to cool the gpu more (if you really want to do this, watercooling would be what you want though from what it looks like, out of your price range)
i would get a new PSU, the rosewill's have worked flawlessly in the past for me, but really are not that good, i would recommend the Corsair 550w
Mine got very warm. Up to around 85C-90C. It started to get really loud. The fan would rev up when it got hot. I blew it out with air duster, tried to do the manual fan thing. Got tired of it, sold it, bought a different card. Overall, it was a great card. If I still had it, I would put 2 more in my case and have 3 4850s on my motherboard. I don't, so I can only dream..