It turned out better than I expected, and my son loves it! I used a mini-itx mobo with an Intel Atom processor. This limited the front ends I could use. I wanted to use hyperspin, but it requires more than my little board can muster. I'm currently using mgalaxy, but I'd like to find something better (and free, I've already overspent on this project).
I did run into some problems during the build. I used weld-on plastic cement to fuse the main portion to the side panels, and it seemed to work well, but I needed to attach the monitor and the rear panel, and I just didn't trust the strength of it, so I ended up using screws. While it's not quite as pretty, I used stainless button head screws, so it's not bad looking. The other problem was with the monitor. I got it for free because it had a bad power supply, and it wasn't repairable (I tried). It ran on 12 volts, so I figured I'd just hook it up to the computer's power supply and everything would be fine. Well, the problem comes when the display and the computer share the same ground connection, and the video cable also carries a ground connection... Horrible lines on the display. I solved the problem by using a second, smaller power supply for just the display and then disconnecting its ground connection through the power cord. Even with these issues it came out really great.
Here's the specs for those who care...
21" LCD 1600x1200
Intel Atom Processor 1.6GHz
2GB RAM
120GB HD
Win XP Pro
mGalaxy frontend
I-Pac VE
2 8-way competition joysticks
18 Happ pushbuttons
Here are some pictures of the build...






If anyone has questions or ideas for different frontends, put them in the comments!