And debian it is!
I've blatantly plugged the DOM into the IDE socket of a standard PC and fired up the ubuntu server installer. You have to compile a custom kernel however, since the stock ubuntu kernel lacks the IDE drivers for the SS4200.
A custom kernel needs to have IDE_GENERIC, IDE_PIIX and BLK_DEV_IDEDISK for the ide controller to be detected.
The E1000 module has the network driver, and the BLK_DEV_DS is quite nice to have USB storage support.
To compile and install I've stuck to this guide, I've used a vanilla linux kernel (22.214.171.124) though.
The tough part wasn't compiling the kernel though. Its getting the BIOS to always boot from the DOM. The RS232 header didn't work for me as described here. I had to resort to a PCIe x1 graphics adapter and do it the old-fashioned way. I've tried to use a straight through cable without success.