Using the helpful instructions in this thread, I was able to install Navit and using the cloudmade download ( http://downloads.cloudmade.com/ ), I was able to put the entire european map on the N900. Thereafter, after editing the various .xml files (maps and navit), I was able to get the thing more or less working.
My main problem is that I can't seem to get the thing to actually use a bookmark to find a destination. When I try the bookmark, I can enter the country OK (France) but thereafter, when it asks for a street, I enter a street and it doesn't seem to do anything with it. Typing a carriage return only displays a little box character but it doesn't seem to want to look for the street. I also find it strange that it doesn't ask for the city first like most other GPS navigation software (there are often several streets with the same name in different cities no?).
I can also confirm that it crashes a lot when launched from the icon (I used the version available in the extra-dev) and a lot less when launched from the command line. It also seems to look for several icons that aren't available even though I added all the xpm file icons given in one of the earlier message - it seems to look for some bar.xpm and shop_grocery.xpm icons in particular...
Overall it's very slow especially when trying to move around the map and/or while zooming in & out.
The software seems promising but still falls short of being fully functional.
Should I try Maemo Mapper instead? Sygic seems like it will be the best thing around but it's rather expensive and still isn't out yet...or maybe I should wait for OVI maps to get on-the-fly routing.

-=AC=-