allow users to assign drive letters to their USB disks

Hi,

It seems users (non-administrators) cannot use their USB drives,
apparently because the system doesn't assign them a drive letter when
they plug them in.

They cannot assign a drive letter themselves either, because they are
not permitted access to the local disk manager service.

Would someone know how I could give them the necessary rights so that
they can plug in an external USB disk and use it, without giving them
full administrator rights?

The machines are XP Pro SP2, in a Windows NT domain (no AD). The users
are members of "Domain Users".

Everything I found on the web or in the newsgroups pointed to the disk
manager to change/assign a drive letter, but this seems to require
administrator rights.

Thanks,

RD