I was wondering if anyone found a way to force the game in windowed mode on start up. The only way that I found to work from the other posts is to press TAB+ALT and then to rejoin the game.

go to your rayman folder and open dosboxRayman.conf (notepad works fine), find fullscreen=true which should be in line 18 and change it to false, this worked for me.

Thanks. That worked perfectly.

I'd do what Maurizio84 says. Although normally, I would just press Alt+Enter. That is the universal toggle between windowed/fullscreen mode.