I was thinking a small v8 engine, scaled down to say 1ft,1ft,2ft height width and length respectively. use the piston holes for air intake, and have hot air go out the exhaust pipes. You should have plenty of room for an optical drive, a hard disk drive, and all the rest of it.
I hope you guys build this, its not as ridiculous as some other peoples so im hoping its a plus. I will have a rough 3d model soon ill post it later.