Omeka has been removed as a One-Click Install from the DreamHost panel. If you wish to install Omeka, contact your web developer or visit the application's website at:
The following is from http://omeka.org/about/:
Omeka is a free, flexible, and open source web-publishing platform for the display of library, museum, archives, and scholarly collections and exhibitions. Omeka falls at a crossroads of Web Content Management, Collections Management, and Archival Digital Collections Systems. With Omeka, you can build many different types of sites. For example you can display collections, build virtual archives, build interpretive exhibits, create teaching sites, and collect stories and memories from your audiences.
Omeka is designed with non-IT specialists in mind, allowing users to focus on content and interpretation rather than programming. It brings Web 2.0 technologies and approaches to academic and cultural websites to foster user interaction and participation and makes top-shelf design easy with a simple and flexible templating system.
Its robust open-source developer and user communities underwrite Omeka’s stability and sustainability.
Until now, scholars and cultural heritage professionals looking to publish collections-based research and online exhibitions required either extensive technical skills or considerable funding for outside vendors. By making standards based, serious online publishing easy, Omeka puts the power and reach of the web in the hands of academics and cultural professionals themselves.