[dnanian]

Are you *sure* you actually came up on the external drive, as opposed to selecting it and *thinking* you're up on it? You can transparently fall back... check the "root" of each drive in the Finder. The one with "special" icons for /Applications is the boot drive... you might want to try ejecting it, too.

Alternatively, you can look in System Profiler. The drive mounted at / is the boot drive, and each drive will give its mount point in the appropriate drive section.

All current information indicates that USB drives are definitely not supported as boot targets under OSX.

(Note: the IOGEAR drives also have problems under Tiger: a lot of people are having issues due to the non-Oxford chipset used.)