I use the Ipaq 3670 with the Destinator software. I have tested the other software available and this is by far the best!!! The Ipaq is the way to go because of the power, memory, and the fact that is uses Microsoft CE. The have just updated the operating system and it is now call Pocket PC 2002. My recommendation would be to either buy the new model Ipaq or to find the 3670 at a good price and get the software update for $29. Definetely get the model with 64mb of ram.
The Destinator software gives you voice turn by turns, address navigation, and many other features. The website is
www.destinator1.com and
www.trackmyvehicle.com One reason this is the best is that they have compression technology that allows you to put more maps on a compact flash card. Currently I have a 340mb microdrive and it holds almost the entire US. They are about to release the new version of the software which will add many more features.
My advice would be to shop around for the Ipaq and the flash memory cards because prices fluctuate and I have found some great prices. Let me know if you would like any further info.
I hope this helps,
Jeff O'Malley