Haven’t had a chance to try it yet, but RoadNav is an open source GPS Road Navigation program that uses TIGER data to generate street maps and turn-by-turn directions, gives verbal commands, and doesn’t require an Internet connection. Also runs on Linux and Mac OS X, in addition to Windows. I usually drive alone, and it’s a *really* bad idea to use a PC-based road navigation program as the driver, so I don’t know when I’ll get around to it. If anyone tries it out, please let me know how it works for you.
Addendum from the comments: Check out this SlashGEO posting for links to other freeware road navigation solutions.
I got this running a few years ago on my SHARP Zaurus PDA (Linux-based). It worked, and the maps were lighter weight than others. There were no voice commands then. If I wanted to use my Zaurus in the car, this is where I would start.
See this post for the other alternatives alongside RoadNav:
http://industry.slashgeo.org/article.pl?sid=06/03/19/215236
A freeware GPS mapping software called OkMap.
If you are interesting to publish my software you can download the pad xml file at http://www.okmap.it/pad.xml that contains all informations.
Thank you
Gian Paolo Saliola