I found another really good method to get Navit to your n900 on www.ethersex.org. Unfortunately there's a mistake in the repo which makes the n900 not to get the Packages-information from it. So I uploaded the necessary files on my webspaces, corrected the error and used the installation instructions but made one change:
Instead of using "http://chollya.org/navit/" as url to repo I replaced the url with "http://chpohl.de/navit_n900/".

I've to mention that I did an installation of a really old navit version from the maemo extra repo before and just updated it with 'my' repo to version 3684. Everything works fine that way but I assume that just do a clean install from chpohl.de-repo will do as well.

Complete installation instruction will be available on my site soon, I'll anounce it here. (That will include tuned configuration of osd and icons.)

Known bugs so far:

• Navit does not give any spoken instructions when not in foreground.
• When media player is running its sound will be muted while navit wants to say instructions (but one cannot hear anything from navit/espeak).

Have fun using NavIt!