After many attempts using various programmes in different modes, I have finally managed to create some decent routable maps for Ireland. I did it thus:

Gathered the data required using osmget.pl (http://forum.openstreetmap.org/viewtopic.php?id=1162);
Combined the .osm maps that were downloaded using osmsort.pl;
Converted the combined map to .mp using osm2mp.pl;
Used mkgmap to convert it to .img format using --route.

Maps generated this way work brilliantly, except that when searching addresses, etc. using the on board menus, my nüvi 200W insists on using the Navteq maps that shipped with it to find as its source - even if these maps are disabled in the settings. Deleting them from the unit (after backing up to my computer, of course!) stops this from happening, but the OSM based maps don't seem to provide any information that will allow address searching at all - or so I thought…

After testing non-routable maps made by CloudMade (http://downloads.cloudmade.com/) and routable ones by Radomir Mucha-Kruczyński (http://emexes.powweb.com/osm/), I noticed that some information in the OSM maps can be used in the Garmin search menus for finding destinations. It seems that mkgmap is filtering them out - I bet there's a simple option that I'm not activating that will do this for me.

I also updated a spelling mistake I made in my last map edit - should be OK now!

P.S. I forgot to say that if you want more details on how I made my maps, just let me know and I'll try and explain the process!

So, after browsing this site for the last couple of months, I have finally managed to join in the fun and contribute! Admittedly it's only a small contribution to start with, as I have no GPS receiver as yet to provide and large-scale additions, but I can use some local knowledge to make additions that I can be sure are accurate enough - such as this addition to the junction of Church View Road and Wyattville Road in Ballybrack (and the addition of the name of Church View Road). I'm still getting used to JOSM at the moment, so this alone took me the best part of two hours! Nevertheless, I'm hopeful that I might be able to make more meaningful contributions without taking up much time in the future!