Hi,
Don't know what CPU you've got, but I've had ongoing heat problems with my 1.4 Athlon Thunderbird. I put an extractor fan in the box and this seems to have solved most of the problems. However, SC does seem to really push the CPU, and with the current (all too rare) heatwave we've got in England atm, I've had to run it with the side off the case to let the heat out. This is particularly applicable if you don't have a full size tower, as the airflow from the case fan is often not great.
I've got a feeling that the heavy CPU usage probably comes from SC being very optimised for lower end machines.