USB drive "Access Denied"

I'm going directly from win2K to Vista, and Vista is having problems with my
USB external hard drive. It is listed under "unspecified" drives in My
Computer, properties shows it having 0 bytes, and any attempt to open or
explore it produces the message:

F:\ is not accessible.

Access is denied.

My investigation so far has led me to believe this has something to do with
permissions, but tinkering with them thus far has yielded no results. Most
of the time, trying to safely remove the device produces the following
message:

Windows can't stop your 'Generic volume' device because a program is still
using it. Close any programs that might be using the device, and try again
later.

I've run every diagnostic I have in Win2K, where the drive reads without
problems, so I'm fairly confident the drive itself is not the issue.