I've got a mini-itx system which I boot off a USB memory stick. I hand built a tiny system which contained a kernel, busybox, freeradius and openssl to work as a wifi authenticator. Worked perfectly as that.

Previously I had tried to make the system work as a video playback machine, but the epia 6000 wasn't up to the task.

I also tried using it as a DVB-S machine but it cooked (and smelled! Probably the DVB-S card, it's an early revision and they run hot) so decided that I'd rather it didn't burn the house down!

The travla is quite a nice case, but there's not a whole lot of space in it as it contains the dc-dc convertor in the front left corner.

I removed the fan from the case, as tman said, it's pretty noisy!

I didn't try a dual PCI, but providing it's supported by the motherboard I can't really see there being a problem.