Is this possible to hide fullscreen window?
How can I do this?

Probably SDL_SetVideoMode with fullscreen=false.

http://tinyurl.com/yad7qwq

I don't remember if it's going to work if you have already called SDL_SetVideoMode; there's probably some existing code in CrystalSpace or Irrlicht that shows how to do this already if you want to go digging.

http://irrlicht.svn.sourceforge.net/view...threv=2914 on line 449 for starters; because irr::CIrrDeviceSDL's constructor has already been run, which will call SDL_SetVideoMode, the rot in the ::run method should be the prerequisites to calling it again to change the video mode. Most of that is probably Irrlicht internals. I haven't read the whole listing, but that's a quick search and a good starting point for you.