I have been encountering this with my new external drive too. I found that it would randomly (or seemingly randomly) freeze the entire computer somewhere between seconds and hours of accessing the drive whether I used Firewire, USB or USB2.
The drive came pre-formatted, FAT32. I have now split it into three partitions and set two of those up as ReiserFS. I have read and written about 40gb of data in an attempt to re-produce the freezes, but so far (lots of wood touching going on!) it has been fine. So far, it would appear that my machine, SuSE 9.2, didn't seem to get on well with the pre-formatted FAT32 drive.
I plan on using the third partition as FAT32 for compatibility with Windows and Mac machines, but I haven't managed to get this sorted yet. That is today's mission.