If you have Dark Age of Camelot and have installed Shrouded Isles you
should use this installer. Otherwise you should download the version
specifically designed to upgrade the original Dark Age of Camelot from
here.

Dark Age of Camelot: Foundations is a free optional expansion to the
online role-playing game Dark Age of Camelot. With Foundations, Dark Age
of Camelot players and guilds can purchase, build, and decorate their
own personal houses, choosing from a variety of styles and hundreds of
exterior and interior objects. For more information visit
www.camelotherald.com/housing/