Editor's note on March 31, 2010: Alfa has pulled the power control driver's from their web site and the explanation is the drivers had some issues the regular drivers did not have. The recommendation is to switch over to the regular drivers available at their web site, Alfa.com.tw.
If you own the 1 watt version of the Alfa AWUS036H wireless USB adapter (came on the market in November 2009), you can now manually adjust the output power in Windows thanks to a new power control utility released by Alfa Networks.
Click here and scroll to the bottom of the page to download the power control software utility program for your version of Windows. Then use this chart to determine how to set the power.
According to Alfa, the default setting is 100% power. You can opt to set it to a lower power if you are within close range of the access point and do not need the device operating at full output power.