[dnanian]

"Any" drive is not bootable. For example, WD externals do not support boot on Power PC Macs. Non-oxford bridges have traditionally been less compatible. Some don't work well with FW800.

While any drive that can be partitioned and formatted properly is compatible with your Mac for storage, startup is different/pickier.

Steps for properly partitioning and formatting a drive (which should definitely be done, regardless of intended use) are in the Frequently Asked Questions section of this forum, right at the top.