Dude, you're overthinking it.
Just get a touch tablet, install the orbiter software on it, stick a wallmount on it.
Talk to tkmedia and get some of our orbiter pads.
But don't waste time trying to build a system, then graft a touchscreen onto it when there are plenty of touchscreen tablet slates out there, _AND_ Orbiter will run on them.
Definitely, if all you want is an orbiter, then follow Thom's advice (I can vouch for how good the WebDT366's are that tkmedia sells) - I thought you wanted a full MD. If you do want a full touchscreen MD, first be aware of how inconvenient it will be to use unless you are mounting them immediately next to you (say on a kitchen bench) where you are moving around anyway... ie it won't be effective in an entertainment environment like a living room, where you are seated out of arms reach. If that is something you want, look up Totallymaxed's comments on the new Asus Eee Top, which is a complete system integrated with touch screen that apparently works very well, at around the US$600 mark or less.