theres special small mobos for things like this.. i dont remember exactly but i remember reading on slashdot lately of something like 200mm*200mm that had 'everything' (gfx, audio & net)..
theres also smaller but with fewer features.(you can make a computer capable of running http server the size of a matchbox.. it was done already years ago)
and about the cdrom, you might want to use an external cdrom drive, some of those have this popup drive like boomboxes.