Here is my first attempt. I'm hardly an ace designer, so feel free to criticize, tell me to junk it etc.
I did try at first to make a browser style button, but it was very hard to make the wine logo fit in a way that didn't look odd, as it's largely a vertical type of logo. Also, is the Windows logo usable? I'd assume it's trademarked or something, but i've seen the 4 colour blocks used in for instance icon overlays in KDE.
If it's thought that this is too large, I can either scale it, or try and make another from scratch that is more button sized.
thanks -mike