Since Kiosk mode seems to be the hot topic of the week (but only because I'm blogging about it!) I thought it would be rude not to include a link to Marcus's Windows Mobile Kiosk blog post. Getting kiosk mode up and running on a Windows Mobile device would appear to be fairly hard to accomplish, I'm in two minds as to whether this is a good thing or not.
First, Windows Mobile is designed to be an open platform, capable of running a wide range of applications and services above and beyond the Office Mobile applications that are included in the o/s image - locking down the product to only run one application would seem to be an odd request especially since there are a number of Windows CE embedded devices that match the hardware specification of Pocket PC but can be configured to only run the one application you need. Also, you would think that many workers might want to take advantage of the built in applications like Inbox, Calendar etc...
On the other hand, Windows Mobile devices tend to be less expensive than their embedded counterparts, partly because the Windows Mobile devices are built for the consumer space and aren't especially ruggedised - perhaps it's cost effective to be able to just throw these devices away if they get broken/damaged while in daily use - There are also some good examples of ruggedised Windows Mobile devices that might provide the ruggedised form factor you're looking for and also includes the Windows Mobile software.