WOW! Blast from the past...
As it turns out, we "won" the senior design contest with our box... here's the basics of the guts:
We later built a nice wooden cabinet to house it in.
It took root-beer from room temp down to ~40F or so as it was being poured... so it worked. I wouldn't reccommend it though... having the compressor kick on every time you pulled a pint was annoying.