Microsoft recently released a new add-on to the Windows Vista and XP Explorer that allows you to edit the picture's metadata. Metadata is embedded text data that is included with every picture to you take with a digital camera, it stores information about the camera, lens settings, etc.
Below is a excerpt from the site: "Microsoft Photo Info is a new software add-in for Microsoft Windows that allows photographers to add, change and delete common 'metadata' properties for digital photographs from inside Windows Explorer. It also provides enhanced 'hover tips' and additional sort properties for digital photographs in Explorer (in Details view)."
To use the utility after you install it, from the Windows Explorer right-click a picture and select 'Photo Info'.