You need to download and installe the following programs:
Efmer TThrottle : http://www.efmer.eu/boinc/
My setup is : use up to 99% of the processors, limit the temperature to 68C. Not that the temperature is 60C, so reaching 68C is unlikely to happen.
Here is the temperature graph over the last 24 hours. The one on the top is the GPU (used at 100%). The limits are 68C and 70C.
If you have more than a computer running BOINC, you need BOINCtasks to monitor all of them from a single point.