Knownothing -
I just wanted to say that although you (I'm sure) are looking for a "cost effective" way to get GPS into your car by integrating it with your computer, it is not the way to go.
If you're doing a great deal of driving I would suggest a real GPS unit, and a real good one.
PC or Mac based GPSs are slow, often inaccurate due to only finding a few satellites and usually don't give you turn by turn directions.
I would suggest a Garmin unit in the StreetPilot Series or the Nuvi series. They are phenomenal units and cheapest at a very reliable seller: shipdog.com
I have purchased 3 GPS units through them. With GPS you get what you pay for, and if you're only going to shell out say $100-$150 for a GPS device and software, you're going to get what you pay for.
Good luck with your choice
I just wanted to add that I'm not just saying this because I love garmin devices; I'm saying this because I have tried all that junk before:
GPS-->Laptop
GPS-->Pocket PC
And the only thing that really works well is a REAL GPS unit.