http://www.osnews.com/story/22750/ReactOS_Proposes_Radical_New_Win32_Subsystem
http://www.reactos.org/archives/public/ros-dev/2010-January/012709.html

It seems that in a few months or so, Reactos will be compatible enough to run gmod. They're planning some radical changes to the win32 subsystem that will bring it up to speed with wine. Maybe in a few years, we won't need Windows at all!