Use the format:
http://yoursite/yourlist/newform.aspx?source=http://yoursite/yourlibrary/thankyou.aspx
http://www.graphicalwonder.com/?p=666
http://blog.mastykarz.nl/imtech-xml-sitemap-free-sharepoint-feature/
http://wael-abbas.blogspot.com/2008/12/change-sharepoint-page-title.html
http://vettekerry.wordpress.com/2008/05/14/add-meta-tags-to-your-moss-site/