Garmin's Basecamp software can be installed on PC or MAC.

It is possible to transfer from Planning Motion to Basecamp on PC, but Basecamp on PC only accepts GPX files.

Since Planning Motion currently generates a KML file, you need to take this KML file and convert it to GPX.

Free KML-to-GPX conversion services are available online.

My Geo Data is one of them.

You can then import this GPX file into Basecamp and then into your GPS device from a PC.