I dont know about the heat of the amd and the intel. The intel conroe shouldn't generate much heat though.
As i told you the intel conroe processors are faster than the current amd processors. I am getting an Intel core 2 duo E6600 2.4Ghz which is something like $343 which as a processor even beats the amd Fx-62.
Under windows xp 2Gb ram is the best amount of ram to have no more and no less.
As a graphics card the 7600GT will meet up your requirments but if you can afford get the 7900GT.
the 7600GT is like $240
the 7900Gt is about $341
The prices i am getting are from overclockers.co.uk. I exchanged the prices to you from british pounds to Dollars.
Depends also what are you going to buy. mobo,cpu and ram or with the case, psu etc etc if so i think you will not afford to buy the 7900GT.