I bought a Garmin 298 from the US last year, and I had a good look around at the time for the cheapest way to get unlocked UK maps for it. I found that there were certain folk that obviously had software that could genetate unlock codes for a small fee. Basically, for any given GPS Serial number and Map product, these guys could generate the unique unlock code to allow you to download and use these maps on your GPS.
I think what this guy is selling is the same - CD with Mapsource and the latest Atlantic charts, plus a code that will let you view on your PC and download to your GPS or data card.
This is probably illegal etc, just so you know.