This page has instructions for how to convert OSM maps into Garmin format: http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin

The easiest option would be download some pre made maps, see this page: http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/Download
It lists which ones include a Mapsource installer. There’s several that include Edinburgh, most have a much wider area as well.

I recommend this website: http://garmin.na1400.info/routable.php
Just pick the tiles you want, fill in your email address, and a link to a Mapsource installer will be sent to you.