If you move a WordPress site to a new URL your internal links and images will remain unchanged, leaving images broken and internal links pointing toward the old domain or directory.
WeblogTools Collection has published a very useful walk through on how to resolve these issues. The article covers the use of a plugin called Velvet Blues Update URLs and Search and Replace plugin to find strings in your database and replace the string.
Full article: http://weblogtoolscollection.com/archives/2010/12/13/wordpress-faq-changing-links-and-images-after-a-move/
WordPress FAQ: Moving WordPress: http://weblogtoolscollection.com/archives/2011/02/27/wordpress-faq-moving-wordpress/
Search and Replace Plugin : http://wordpressinfo.com/2010/04/04/search-and-replace-database-string-plugin-for-wordpress/
Velvet Blues plugin: http://www.velvetblues.com/web-development-blog/wordpress-plugin-update-urls/