A couple of OpenGL multiplexers for Xen (and VMWare, theoretically) exists: http://www.cs.toronto.edu/~andreslc/xen-gl/ http://www.diku.dk/hjemmesider/ansatte/jacobg/gfx/
They allow guest virtual machines to render 3D graphics using the host machine's graphics accelerator.
I think they are very interesting in combination with Wine, because Wine can let Direct3D games run on top of OpenGL, making the multiplexers work for all modern games, whereas running a real Microsoft Windows guest would only allow acceleration for some games.
There's a list of supported XGL versions and GL calls on this page under "Capabilities": http://www.cs.toronto.edu/~andreslc/xen-gl/
And a couple of whitepapers here: http://www.diku.dk/~jacobg/blink-techreport.pdf http://www.diku.dk/~jacobg/blink2.pdf
Will WineGL run on top of a multiplexer, or does it lack support of some calls?