I think he wants to be able to open a program from the console in X.
& is what you're looking for.
"firefox &" will allow you to open firefox from a shell but when the shell closes it does not close firefox.
Of course firefox is just an example, & is the important part.
Note: After issuing a command it may not immediatly return you to the prompt. Hit enter a few times, then you can exit the shell.
P.S. Screen is an awesome utility, so I'll give that an honorable mention.
