I'm having the same problem with my Oxford 911 enclosure. USB 2.0 works fine; firewire doesn't work in either XP or Linux.

Raptor: I agree about the 4 pin plug being a POS, but you're wrong about USB 2.0 being better than firewire. It may have a higher theoretical bandwidth, but firewire enclosures (specifically those that use the Oxford 911 chipset) have significantly better real-world performance (on the order of an additional 5-10+ megabytes per second, IIRC.) Note that this shouldn't matter for optical drives (too slow for it to matter), but it absolutely does matter for 7200RPM 3.5" hard drives.

I have just such a drive, and for my purposes transfer rates are very important, so "just use USB" isn't really an option. I paid extra to have both connections in my enclosure, and I expect both of them to work...