i am assuming the only change both of you have done to your computers are os updates? if so then that is likely the problem.
one way to check is to go into system profiler and see if the drive is being recognized under the firewire bus. if not all it will read is something like 'maximum speed: 400 mb/sec.
as with any os update, some changes will improve functionality, and some will not. as this most recent update is pretty intensive, it wouldn't surprise me if the developers missed a few things(read some of the problems some people are having with ilife 06).
i would first check with the drives manufacturers for firmware updates (you may need to apply them using a PC as most seem to be only available in that format. if that doesn't help there are numerous apps on the market to help trouble shoot/repair these types of problems, but if it truly is 10.4.4 related, they might not be up to date yet on working with the new protocols and structures.
one last thought, double check to see what position the jumper pin is set to on the drive itself. i too have an external case (firewire) with a maxtor hard drive within, and thus far no problems. but when i initially set it up it wouldn't register unless the jumper pin was set to master - same thing with my other external case and dvd burner. try changing positions and see if it gets recognized.