Is there a program much like a on screen keyboard which only types in keys for a certain program?

For example: I'm running an mmorpg and have 2 "windows", unfortunately, When I press space bar, it will only register to the window which is open or active. I was hoping there will be a program much like a on screen keyboard, so that when I press spacebar or hold the said key down, it will be registered to both windows. I'm looking for a keyboard (freeware please :p) which will work on a certain program so I can tab out and multi-task.