Micrososft Research provides a free barcode scanning application for Windows Mobile 2003 and 5.0 based Pocket PC and Smartphone devices called A.U.R.A, enabling a user to scan bar codes of objects with a camera and decode the details associated with the object such as price, manufacturer, etc. (via)

A.U.R.A requires a macro high res lens to convert the bar code image to a decoded string. So if your Windows Mobile device does not have a lens that cannot focus at the close distances required by A.U.R.A, you can send a self-addressed stamped envelope to Microsoft and they will ship you one.

Project A.U.R.A. Lens Kit Request
Microsoft Research, Community Technologies Group
One Microsoft Way
Redmond, WA 98052
United States of America

Download from here