>> Is XML only used on the backend? Which means, no matter what the client is using, we can use it right now as it's not something that the browser has to support.

You can use it on the client and the server. Let's say you had the UT in XML format on the server. You could detect if IE5 is being used. If IE5 is the client, then you could return the XML embedded in the HTML (called a data island) and you could reference an XSL document on the UT web server that would transform the XML into DHTML on the client. You could then have multiple XSL files on the server, and either based on forum, preference, or even a drop down, you could update the DHTML on the client by just executing divMain.innerHTML = oXML.transformNode(oXSL)

If they had Netscape browser, you could simply do the .transformNode() on the server (like in an ASP) and return HTML, so that the client wouldn't see the XML. You just need either IE5 or just the new MSXML parser on your server, and you can then execute CreateObject("Microsoft.XMLDOM"), and you're done. If you program in Java on the server, you can download the same parser used by IE5 from http://datachannel.com which DataChannel created with Microsoft, same exact interface.