Let me throw my tuppence worth in:
1. I will never buy any software for satellite car navigation due to the inherent inaccuracy of the map data. I would imagine that you really require this type of software when you are totally unfamiliar with a place and you need to find your way around. Given recent changes to the one way system in Edinburgh, this would be impossible.
2. I run with my Dell AXIM A30 protected by an aluminium case and a Globalsat BT338 inside a bumbag. I use Memory-Map navigator software for the OS maps - you can get 1:50000 and also 1:25000. The BT338 is superb, keeping fixed to the satellites even in wooded terrain.
Hope this helps.
Useful sites in UK:
http://memory-map.co.uk/
http://undercutter.com/