Ryan,
Confirm the Garmin GPS model supports NMEA protocol, in addition to support for Garmin protocol. ArcGIS for Windows Mobile application and runtime SDK use the same API to communicate with GPS receivers supporting NMEA protocol. NMEA does not enable ArcGIS for Windows Mobile to control the settings of a GPS that supports it. To do this, a third-party tool must be used that uses a two-way protocol, such as Trimble or SiRF.
Cheers,
Denise