Something I setup for a friend the other day is using ResizeEnable: http://www.digitallis.co.uk/pc/ResizeEnable/
This lets you resize applications, even if windows doesn't allow you to.
Of course this may not necessarily be the same as fullscreen, but you can technically just resize the application to your entire screen.
This is also really handy for VN's that have a fixed resolution that the game doesn't let you change : p