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GPSDrive is an early port of an excellent moving-map GPS system. It easily paired with my Socket Bluetooth GPS with little configuration hassle, then proceeded to download maps over WiFi. It was almost too easy :-) A quick push of the "fullscreen" button on the Nokia brings the map into full-screen mode. The software is still pretty beta, but it worked well enough to take me on a 1200mile+ drive last week!
I picked up a suction-cup radar detector mount from Radio Shack, and modified it to allow me to attach my Nokia 770 to my windshield just next to my rearview mirror. The software did a great job of showing me exactly what highway I was on, and I could easily see my turns well in advance. At one point I missed a highway (at 3am in the middle of the desert), and I easily found an alternate turn to get me back on track. This was WAY easier than paper maps.
Nokia 770 Download Link:http://www.elisanet.fi/tapio.tolvanen/nokia770.html
Main Linux GPSDrive Home Page:http://gpsdrive.kraftvoll.at/index.shtml