1. Download the binaries or compile them within your scratchbox environment.
2. Install navit and optionally support for garmin maps
3. Configure navit
The simplest way to get navit up and running is to use Open Street Maps as it is free and open source.
To do that, you should download a binary version of the map so it is ready to be used by navit.
1. Edit navit.xml (must do this as root so the changes are saved, you can achieve this either by using SSH or become root). 1.a Replace the path to the map file:
<mapset enabled="yes"> <map type="binfile" enabled="yes" data="/media/mmc2/map/planet.bin"/> </mapset>
For me, I put my planet file on the memory card in a folder called map.
Notes: The navit project now has a project page on the maemo garage site, https://garage.maemo.org/projects/navit/. The first binary version of navit for the Internet Tablets was created on another site, http://www.tecdencia.net/navit/.
If you want to build navit yourself, you need to have scratchbox installed and should execute the following:
You just have to build last version with this option : --disable-binding-python --disable-gui-sdl --disable-samplemap --enable-avoid-float --enable-avoid-unaligned
Additional tips for this specific platform may be added. Feel free to contribute!
Some additional details (Nov 28, 2008): I spent an evening getting Navit working on my N800, here are what else you need to do on Diablo with a Bluetooth GPS 1. Install bluez-utils-test, have to get this from a Chinook repository for now 2. Follow the instructions here  3. Change your navit.xml vehicle definition to use file:/dev/rfcomm0 instead of gpsd Now each time you start Navit, the GPS connection gets made for you. This avoids workarounds such as starting Map or gpsview.