His memory will be doubling, his hard drive space will be increasing by 25%, and his processor speed will be increasing by 73% (based on clock speed). He'll also be gaining USB 2.0 capability (big help with podcasts on the new iPod- he currently only has 1.1), and the ability to burn DVDs (dual-layer, no less!).
I had two people express interest in his old chassis within an hour of making the order and several others since then, which makes me feel good. I think it's pretty much spoken for, however.