You can set the intensity for how you want to mine in CGMiner. It goes from 1-20, with 20 being your-computer-is-unusable tier (seriously, I've never heard of anyone running it at 20).

I have two settings going, one for 17 intensity which has my 5870 mobility running at about 93-97 C, and one for 12 intensity that I can leave running while I use my computer, which usually puts me around 83 C.

I use it for litecoin mining, but I think you can use it for bitcoins as well.

You can use CGEAsy to set it up if you're unfamiliar with editing batch files.