I recently installed Windows 7 as the OS for a PC that I'm using as a media center running XBMC. Initially I only put in 2 speakers. Now I've added rear speakers. The soundcard is a SoundBlaster Live ...
In Windows 7, you can go to Sound configuration, select your speakers and click Configure. You will then get a dialog called Speaker Setup. You start with a question about Audio channels (Stereo, ...