A tip for anyone else who has been having trouble getting the Jmap utility (used for zooming in on map images or any other image,actually) to install :
The ipk file has been stored as a tar file instead of gzip and won't be recognised by the package installer so gzip the package then rename the file back to the original name. It then installs ok.
gzip jmap_20030109_arm.ipk
cp jmap_20030109_arm.ipk.gz jmap_20030109_arm.ipk