I am jumping in late, but the way I understand it...
You have a monitor designed for mobile use. It has the regular ground wire and two 12v inputs (kind of like your car stereo receiver).
I don't know why it would need the second one unless it has a clock or tuner or something like that.
Anyway if you are sure they are both 12v inputs then you can just hook them together up to the 12v source.
you can use the same for your house...just get a 12v adaptor (you probably want a 1 amp version)...but check to see if you already have one lying around.
Your computer power supply really isn't designed for so much drain.
My little 4" lcd pulls about .5 amps.
------------------
http://www.geocities.com/mr_bubba_zanetti/