I suggest you buy the book called
Programing Windows CE.NET by Boling. It is the "Pocket PC Programming Bible" so far as I'm concerned. Lots of examples and it covers most of what you'll probably need.
Next, you can download the latest Pocket PC developer's tools from Microsoft (for free). If you want to develop using C or C++, download the Microsoft emBedded Visual C++ 3.0 from
www.pocketpc.com developer's page. Using this tool will allow you to create applications for the older Pocket PCs running the original OS, as well as the newer 2002 and 2003 OS devices.
Now, if you've never programmed for Microsoft Windows, then I suggest you also buy the book,
Programming Windows by Petzold, which truly is the bible for windows programming.
Good luck with your endeavours!
ppcinfo