This is very unlucky. I hope you get it sorted. I've had a LaCie mobile drive (FW400/USB 2.0 - 40GB) for probably five years now. It's been dropped from a great height like most of my portable stuff and survived, and has always worked a dream after some initial disagreements it had with OS X 10.2. I also use a desktop IOMEGA (FW400/USB2.0 - 250GB), which also works without a hitch plugged into my iMac.
In the long run I can safely say that you won't regret the switch, once things are running smoothly they run smoothly for a very long time.
In the long run I can safely say that you won't regret the switch, once things are running smoothly they run smoothly for a very long time.