Just for the record, Zzzy instructions worked *great* for enabling a Holux GR-213 ("GPS mouse" serial receiver) plugged into a Nokia N800 using a Holux USB adapter cable (which contains a Prolific PL2303 serial-to-usb chip): maemo-mapper is working wonderfully.

If afterwards it stops working, just see it the /var/lib/gps/.gps_no_serial_ports is back there, and if so, just remove it and restart maemo-mapper. That happened to me, I think some program in Maemo recreates it from time to time.

Cheers,
--
Durval Menezes.