I use the Mitac Mio168 with Co-Pilot Live. Comes with all the bits for attaching to and unattaching from the car. perfectly audible over road noise (unless you insist on driving with the window wide open!). So far it has only led me up the garden path once. Try an outfit called Global Positioning Systems (one word) in the UK.
By the way, the pocket PC runs Microsoft software but you can't have everything!