Memory-Map Navigator for PC includes the ability to connect to older Garmin GPSs that support the legacy Garmin protocol via serial port or USB. However, these days we cannot guarantee any compatibility because the standard protocols are no longer used in all Garmin products.
The best way to exchange overlay data between Memory-Map and your Garmin is to import or export GPX files. Garmin, and many other manufacturers, support GPX as the standard for sharing routes, tracklogs and marks.
When using GPX in Garmin's own software and web site to program your GPS, you should contact Garmin if you need support.