I'm having a bit of trouble here while playing in Windows 7... I can't put the game in windowed mode. When I launch the game I go to the Options section and try to uncheck the "Play fullscreen" option. It says that I have to restart the game, I do it... But the game re-launches in fullscreen again.
Works fine here... the UI is a bit confusing, do not uncheck "Fullscreen mode", just check "Windowed mode" and after the message, restart.
Confirmed this worked for me as well, just check the windowed mode and it automatically unchecks full screen and after restart is working in windowed mode successfully.
Though I had a bit of trouble once in windowed mode to resize window to fit screen since there is no resolution option to set the window size it defaulted larger vertically than my widescreen display could show in windowed mode. But was able to drag window border to resize and the top menubar popped into view. Was then able to drag around the screen and resize like a normal window successfully; but, be aware at least on my system the mouse cursor disappears at you hit the window for Unepic but if you click right at the edge it does switch the cursor to the window sizing cursor and responds normally and clicking into the title bar does reposition the window even though the cursor disappears until you hit the inside of the game window.
Only bad thing is that window size settings do not appear to be retained on exit, so if you have it set to windowed mode you'll have to reposition/resize your window again should you want it different than the default window size & location.
Haven't figured out if respect the ratio video option would help, since it just seems to make the in game menus and UI resize respective to the window sizing if turned on and doesn't seem to affect the window itself at all.