I was thinking the Shuttle small form factor modified would work,
The mods are pretty basic, but with the size of the little thing, would require a different case cover. The mods are basically this, to put a Panaflo L series 80x15mm side intake fan were the video card is located and put in a 300 watt Seasonic were the little power supply (with that horrible 40mm fan) is located.
If I took the stock cover off and made one that was wider to clear the added 15mm thick fan on one side and the larger Seasonic power supply. Actually, I would prefer to use my Antec Trupower 430w for the extra ventilation and case fan controls (A little louder but I like the temp controlled case fan option) Put in my Samsung CDRW/DVD combo drive, a memory card reader in the floppy slot and strap the floppy inside somewere (in case I need to use a floppy once a year)
With the increased flow and decreased temps afforded by the silent intake and quiet power supply fans, the BIOS will see lower CPU temps and slow the CPU/Exhaust fan down. The added airflow would be nicer to the suspended/side sinked hard drive and combo drive. A Radeon 9700 AIW with a Zalman (cooled aided by the Panaflo blowing on it) The video card's mass is a concern, I will bolt a bracket on the card to hold it in place.
The main thing is to figure out how to get the power supply to fit in it. Aluminum channel, rivets and custom sheetmetal work would do it. The added width of the thing is not too bad, I could make a custom front panel addition to hold my temperature monitor displays and maybe mount the floppy drive sideways.
Slap in the nForce2 all in one mobo, put the Barton cored Athlon in place (burn it in and drop the voltage a bit) dual 400MHz DDR memory and it will be done. The ultimate, small and quiet multimedia box!
Anyone out there have one of those little boxes to let me know how much fabrication I would have to do to fit a normal ATX power supply in it?