As JW says, but you'll need a garmin - garmin lead.
In the absense of same, there's a free download called "EasyGPS" ( http://www.easygps.com/
) which is a basic Waypoint / route manager. It's designed for geocachers, so a lot of useless rubbish for boating, but it does what it says on the tin - namely talks to umpteen flavours of satnav, and saves edits wayoints, so you can easily rename stuff and have a backup on your PC should the Garmin go pear shaped or overboard. It also means you can use the Garmin - PC lead you probably got with the unit at no extra cost!