The HP MediaSmart Server Fan Control addin for Windows Home Server can control the speed of the fans to suite your liking. The interface features sliders to adjust the parameters for Constant Fan Speed, Fan Speed Adjustment and Threshold Temp Adjustment. It also has buttons for Factory Defaults and Optimized Defaults. I tried various settings and even put the fans down to the lowest permitted setting (25% of full speed). This immediately rose the temperature of the CPU to about 42° within 30 seconds, so I quickly put them back to optimized defaults!

More info: HP MediaSmart Server Fan Control