We use Microsoft Streets & Trips with a GPS receiver (BU-303) on our laptop
Works ok for trips wouldn’t want to use it for everyday driving, no voice commands etc.

From searching here and other forums looks like an OEM NAV is theoretically possible for about 6K $’s

Try here for more info/options

http://www.mp3car.com/vbulletin/forumdisplay.php?f=24

or here if you have a PDA

http://www.gpsinformation.org/dale/PDA.htm