So humans are around 150 watts?
Depends on the physical activity. An adult sitting down resting radiates about 100 W or 1 W/kg (depending on which study you look at, the latter is the more recent approximation I think).
However it depends heavily on the physical activity. Sweeping floors ~twice the heat, climbing stairs ~14 times the heat output
superglue a couple of Ninja's to your head and you'll be amazed at the difference.
----but......as to the main point...if you are going with a 400 dollar overclocked cpu and a 400 dollar mega vid card to do a gamer super-rig,it makes WAY more heat than a vanilla Sempron machine. Getting the excess heat out of the case-into the room-then becomes where you get NOISE,because a Hot Rod puter won't cool passive.
Now there's even single core AMD 65nm cpu's,similar to a Venice 3000 but even less power hungry and cooler. These will,especially if undervolted,hardly warm a Ninja. They may not have the "power" of the Ultra-Gamer-Beast machine---yet will blow away the XP's and P4's that were the Gamer machines a few years back,can EASILY do damn near anything most folks need-perhaps taking 5 sec longer.....but at less cost/heat/noise
For WAY CHEAP...you can get the "Low End" AMD and it's about the best cool-quiet going,probably heats the room less than a typical P3
The X2 or Core 2 chips are,for their performance,pretty good in terms of heat,but heat/silencing is always a trade-off. So, the key is avoid performance overkill