Designed by Sun Microsystems and Netscape as an easy-to-use adjunct to the Ja Va programming language, Java Script code can be added to standard HTML pages to create interactive documents. As a result, Java Script has found considerable use in the creation of interactive Web-based forms. Most modern browsers, including those from Microsoft and Netscape, contain Java Script support
With Java Script you can do cool things on the client that avoid the need to make extra trips to the server.
The decision to use Java Script or JScript should be based on the browsers that view a site. If the site only has an audience of IE 3+ people, then JScript is fine (or even preferable because of additional features over Java Script). If the site's audience includes non-IE user's, Java Script must be used since non-IE browsers don't support JScript. -- Gene Berger
Sites with good cut-and-paste code for Java Script and ?DHTML