I have similar problem. I just purchased Buffalo HD-PX320U2 Ministation 320GB.
I'm using Vista SP2 and when I plug in the drive, it freezes the window explorer and Disk Management shows up blank.
If the drive is plugged in during the reboot/boot it freezes the window after logging in.
After 5-10 minutes or so the drive shows up on the window explorer and everything seems to go back to normal.
If this problem persists, I'll be returning the drive.