I was also experiencing the Macbook high cpu temp and fan speeds problem. The fans would run at hight speeds even when the computer was idle and there was no programs running. According to istat menu the fan was constantly running above 6000 rpm.
A common problem appears to be a job in the print queue but this was not the case and there was no obvious culprits in Activity Monitor consuming the CPU ( remember to change it to show All Processes )
I reinstalled Snow Leopard on the MacBook but this made no difference as the fan continued to constantly run at high speed.
The solution for me was a comment buried in this discussion
It turns out some times the fan gets stuck in the high position. All you have to do to reset it is turn the computer off, remove the battery, disconnect the power adapter, and hold the power button down for 5 seconds. The problem disappears when you start your macbook up again.
This seemed like an unlikely solution and explanation but I tried it and the fans are no longer running at the high speed.