SuperCollider for Windows (Psycollider) is available from

http://sonenvir.at/downloads/sc3/sc3-win/

as a complete package coming with sciss' SwingOSC as a GUI engine.

The latest binary is also available from the sourceforge page:

http://sourceforge.net/projects/supercollider

For build instructions and further information please read the readme.txt file in the package

a discussion forum for sc on windows:
http://www.crm1opdracht.tk/