Thanks - I'll keep posting updates here, in that case.

It is actually possible to use OS 1:25k maps in Mappero, if you start off with a georeferenced TIF file. These are available in 10km x 10km tiles, with world files available from the OS.

http://www.ordnancesurvey.co.uk/oswe.../techinfo.html
http://www.ordnancesurvey.co.uk/oswe...boutpopup.html

The tiles can be purchased from http://www.mapyx.com/index.asp?tn=productview&pid=6635 - although you could probably stitch something from http://www.ordnancesurvey.co.uk/oswebsite/getamap/ (or multimap). Unfortunately if you want to buy a large area (eg the Lakes), it would be quite expensive.

I convert them using GDAL tools in linux - but I'm not sure how to do it in windows. I'll post a recipe later.

The trick is to split the area you need into tiles and then write them into the Mappero cache directly.