You could also use the USB mass-storage class spec (bulk-only). There is class driver support for that in WinME, 2k, XP, and later OS's. (I think it's also in Win98, but my memory is failing me on that point).

USB Mass Storage (Bulk Only) Class Specification:
http://www.usb.org/developer...ulk_10.pdf

The downside to this approach is that you'd also need a decent understanding of the SCSI block command protocol (SBC-2 or SBC-3) unless you have some back end hardware that can take a CDB directly.

Just an alternative that may or may not meet the needs.