Sounds like you may have NS or your GPS configured screwy. Check out Blackwave's recomendations here:
http://forums.netstumbler.com/showth...ng+serial+port
There is gigabytes of pages on here relating to setting up a GPS, I recomend searching around. You'll see many people advising using hyperterminal to view the NMEA sentances from the GPS. Try it, then you'll know if the pair are talking to one another.