USB drive letter resevation

We are using Windows XP on a Novell network and are having problem when connecting USB devices. What happens is that when connecting an USB device, no matter what of type (even on a newly loaded machine) the assigned drive letter is F: but F: is in use by the first Novell networkmapping. When checking in Disk Management, all drives except floppy, hard disk and CD-Rom are available to be assigned to any device. To me it seems that Novell is not reserving the used drive letters or does not inform Windows about the drive letters it used for the Novell drive mappings. Maybe something in the Windows registry but I have no idea where to start looking.
When connecting a mamory stick, windows assignes the first "free" drive letter, once I've changed the drive letter for a certain device and reconnect it later there is no problem. But each new device I connect gets the first "free" drive letter from windows however that drive letter is in use by a Novell network mapping.
Has any one seen this before? Please help ...