This is just something I need twice a year and was always too lazy to find. Bookmarked.
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).
Microsoft Photo Info runs on 32-bit versions of Windows XP (with Service Pack 2 or later) and the Windows Vista operating systems.
(found via LifeHacker)