Was the drive SATA? Is that why you couldn't just connect it to the internal IDE bus?I tried everything under the sun to get my MDD FW800 to boot off of USB but it absolutely refused, it would start to load the OS installer and I would get the gray "Stop" sign each time. I tried it with a few different drives.
I finally borrowed an old FW drive enclosure from one of my friends, used one of the HDs I had tried in the USB enclosures, and it booted up in target disk mode no problem.
I wouldn't say "can't", but I'd agree that it's non-trivial.Apparently MDD FW800 systems can't be booted off of USB.