This is an easy way to control fan speed and lower temperature on ATI HD 4850/4870:

http://forums.guru3d.com/showpost.ph...69&postcount=8

youtube tutorial:
XP:
Vista:

I made for me two profiles Fan30% in idle with VGA temp of 57/58° and Fan35% in full with VGA temp of 52/53°.

Enjoy. THX 4S_Nero