Jovy, do you mean XHTML rather than XML? At the moment, we're some way off authoring pages using XML.
If you do a spot of research, you may find many business systems using XML as a basis for their corporate information storage and it's excellent for data structuring, but it's a long way from being adopted as a web authoring language... I'm not even sure it will ever be, because those aren't necessarily XML's strengths.
XHTML however, is the latest standard for authoring web pages, and this is what you should be using to write your pages. A well-formed XHTML page should view consistently in any modern browser, providing you've followed the correct
syntax (dictated by its
doctype).
Paul