Jinkster, the Garmin site has a downloadable specification for the comms protocol which you might be interested in. As swh says the communications is fairly simple - the spec' explains it clearly in a "C" programming language type format.
You can either write a simple (ish) programme in something like
VB or Labview to communicate with it or if you don't want to be bothered you can buy an interface programme from a number of websites for about £25 or so.