if you start something in the foreground and then decide to run it in the background, press Ctl+Z to pause it, then type "bg".
And if all you want is the straight console, you don't have to change runlevels. X-Windows leaves one console open if you use the GUI runlevel (5 in most distros, i believe) on console 4 (press Alt+F4). Press Alt-F7 to get back to the GUI. I prefer to boot up to 6 consoles and run X manually so I always have at least three consoles available for root (multiple mc's that behave intelligebly for example). Just don't set the default runlevel to 0 or 6; that would suck most humourously.
-t.