Meanwhile, there’s a single-click-installer for Navit on the Nokia internet tablets. It will run out of the box without any further configuration, showing some place in southern germany. However, you may want to install maps covering the area where you live.
Navit reads a couple of formats, including Garmin maps and (of course) openstreetmap maps. If you want to play with it on your tablet, see the dedicated documentation in the wiki of the navit project, and this thread on internettablettalk.com.