Checking the Version of Pocket PC OS

On the Pocket PC Start menu, tap Settings.

Select the System Tab, and tap on Asset Viewer icon.

Maximize Version, and look at the OS version information.

Win CE Version	Pocket PC Version
5.0	Windows Mobile 5.0
4.21	Windows Mobile 2003 Second Edition (Pocket PC 2003 SE)
4.20	Windows Mobile 2003 (Pocket PC 2003)
3.0	Windows Mobile 2002 (Pocket PC 2003) (will not work with Pendragon Forms)

Source: MS Windows Mobile Developer FAQ,

To find the Model number of your handheld device, maximize System and look at the Model ID information.