Hello Squire, allow me to now allocate you as my official 'Garmin Guru' and IT guide. If you choose to accept i would greatly appreciate it if you can help me gain some knowledge while I'm away for the next two weeks with work.

So far i have followed your info and gone to OSM site, i have built around ten maps so far of the world ( excluding Africa to date ) using the grid system and downloaded them. They are sitting there in a file along with my 'Basecamp' and 'Mapsource' downloads. I have bought my Garmin with me and a USB plug in hard-drive.

Ok, whilst writing this i have been flicking through the posts following on from 'colebatch' and my brain is getting fuddled somewhat by all the advice. As per usual i get 'brick walled' by a simple issue. This time it's which correct file to download from OSM from there list. I assumed when i looked at the options that it was the 'osm generic windows.exe' file that stated 'map installer for Basecamp/Mapsource on the windows' blah blah etc etc and continued to download.
Since reading some of the posts which mentioned 'zipped' files i now feel i may have downloaded the wrong files. Having said that a few of the maps didn't have the 'osm generic windows.exe' file showing in the options and then i downloaded the 'zipped' file and have a mix waiting for the next stage.
I have opened my Mapsource several times and as per 'colebatch' said in stage 6 they should appear in the map drop down selector at the top, i cant even see this drop down selector....!!! (does he mean the box to the side which gives 'maps, waypoints, routes,tracks'..???
Here below are a couple of screenshots of the OSM file options they sent.