From the Minnesota DNR web site:
This extension was built to provide users the ability to directly transfer data between Garmin GPS handheld receivers and various GIS software packages. Using this program a user can use point features (graphics or shapefile) and upload them to the GPS as Waypoints. Line and Polygon Graphics or shapes can be uploaded to the GPS as Track Logs or Routes. Conversely, Waypoints, Track Logs, and Routes collected using the GPS can be transferred directly to ArcView/ArcMap/Google Earth/Landview and saved as Graphics or Shapefiles.
This program has a real-time tracking mode that allows users to follow their progress on the ground within an ArcView View Document, ArcMap Data Frame, or Landview Map. This real-time track log can be saved as either points or lines as a set of graphics or in a shapefile.
At this time DNRGarmin contains (but is not limited to) the following functionality:
Download Waypoints/Tracks/Routes – Download waypoints, tracks, and routes from Garmin GPS and save as ArcView Shapefiles or Graphics
Upload Waypoints/Tracks/Routes – Upload waypoints, tracks, and routes to Garmin GPS
Real-Time Tracking – Collect real-time locational information and store as graphics or shapefile
Waypoint to Point – Converts Waypoints downloaded from the GPS unit into a point shapefile or graphics
Track to Point/Line/Polygon – Converts a Garmin Track log to an ArcView graphic or shapefile
Point to Waypoint – Convert Point shapes or graphics to a GPS Waypoint
Line/Polygon to Track – Converts a line or polygon to a Garmin Track
Point to Line/Polygon – Converts Point themes to Lines or Polygons
Add Documentation to Features – Adds basic documentation to ArcView themes including Name, GPS Model, Date, Agency, etc. – ArcView 3.x only
Calculate Shape Attributes – Calculates Area, Perimeter, Length attributes for features. ArcView 3.x/9.x
Calculate CEP – Determine Circular Error Probability rings for Error estimation. ArcView 3.x/9.x
Image Hotlinking – Create hotlinks between images and GPS data.
USB Connectivity – Speed up your downloads by a factor of about 10 with USB connectivity option!
Projection Engine – Built in Projection Functionality using Proj.4 Cartographic Projections Library http://www.remotesensing.org/proj/ by Gerald Evenden