You'll need an "e4690" (dual DVI Video card) in the Brain Box, DVI to VGA Video Cable(s) and a 20" MLD monitor. Depending on which lower Door you have, the monitor may drop right in, or you'll have to get the Dremel out and "modify" the lower door opening a bit. You do NOT need Dynamic buttons, but they ARE nice to have. ;-) Oh, and bump up the RAM to 4GB - it loads faster and alot of games will no longer "lag" during play.
When searching out a video card, be sure you get the "PCI Express" type and NOT the "AGP socket" type. AGPs go in 2.5 boxes, I believe.