If you have that hooked up to your computer, you can get a capture card for the computer and hook up the consoles to it that way. One such product which claims to be for such a purpose is the Adaptec GameBridge.
Alternately you can sell your monitor and buy a TV. Better yet, sell it and buy a monitor WITH inputs. My wife's Dell 2007FPW (20" wide) has VGA, DVI, composite and s-video inputs.