Howard,
have you considered cracking open the GPS unit and checking if it's
maybe just a USB-serial converter in disguise? Maybe you can just tap
the UART signals somewhere and splice in a 232 level converter or
something like that.
- Marcel
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist