http://bugs.winehq.org/show_bug.cgi?id=5341
--- Comment #10 from Mike Kristoffersen wine@mikek.dk 2011-04-18 03:40:14 CDT --- I haven't been able to make this work for years, but playing around with it, I just found a way to trick it into docking.
On a windows system you would drag the window to one of the boarders and it would then snap-dock to the boarder - what you need to do in wine is not to drag the whole window, but rather click in the area to the left of the source insight defined "min-max-close" buttons (I don't mean in the title bar, but right under the title bar), then you can dock the window.
I tried this with the "project" window.