The GPU usually sits around 40 degrees celcius while the other number (TMPIN0) sits around 65-75 for normal computer use, in game it goes as high as 86-88.
Should I be concerned about the temp?
2) I started looking into this because I took apart my ATI Radeon 5850 - I was reading on how to get better performance on a game and a forum thread talked about opening up the graphics card and completely cleaning out all the dust. I did that and noticed there was thermal paste... and that scared me.
A friend of mine said that I might be able to get away with just putting it back together, instead of cleaning off the old paste and redoing it. Is this running too hot now?
Compared with modern cards, like the HD 7000 series, your card is quite hot, but 88C is relatively normal when gaming on an older card. If it was running at 88C with the thermal paste, I would definitely reapply it. Here's a decent tutorial: http://www.youtube.com/watch?feature=player_embedded&v=...
Also, if the temperature really is worrying you, maybe buy an aftermarket fan set for your model of Graphics card
Those temps are pretty high, and I like to keep mine under 80 at full load just to be safe. Other people would say under 100 but I like to keep a pretty big buffer. I would get GPU-Z to check your temps, as I have had issues with HWMonitor (Although over all its fantastic) Also in GPU-Z, you can adjust/monitor fan speeds.
As far as re pasting it, I wouldn't worry about it. I have taken several GPUs apart several times, and NEVER noticed a change in temps/performance.