It all depends on your system specs and what game you are actually playing and on what settings, but with the specs stated I would think only the new games like Doom3, Halo2 and HL2 etc. would require a constant 100% cpu usage.
Another thing I would suggest is checking your CPU temperature, if its running 100% and stays cool then theres no problem, but recently I tested mine and found it went to about 85 degrees when playing CS, which is well above the recommended safety levels.
I thought that it would use 100% as it will try and get the most fps possible. If it isnt, than there is probally something bottlenecking the performance, or it has a limited frame rate.
why do i get like 80fps on quakeIII and 10 on command and conquer? Is my videocard the bottleneck?
i tried oc-ing my video card and when i play a game, it resets itself. It ran stable at 250mhz and 200mhz memory. when i turned the game on, then checked the frequencies, they were back to default.