How to read/write Route information to/from a GPS unit?

Question

Hi,
I am building a new application (Forms) to display GPS information etc on a laptop.  I have been able to parse teh NMEA stntances and grab the information I need BUT now I need to download/upload the route information to/from the GPS unit.
I have been unsuccessful so far in finding any code examples etc to help me.
Can anyone steem me to something?
Using VS2008, C#, .NET 3.5, Visio.
Thanks
Phill