HTML is not XML.
You *can* have XHTML that is XML-compatible, though.
But there are many rules in XML that are not necessarily followed in HTML.
If you use XHTML in strict mode and validate it (say with the w3c validator) *then* you can probably treat it as XML for the purposes of this usage.
Understood re: html not being xml. In terms of using xhtml, is there an easy way to convert an html file to an xhtml file?
Well, to begin with, all tags should be lower case. <td> instead of <TD>.
And all properties MUST be enclosed in quotes, not apostrophes. <td class="whatever"> and not either <td class=whatever> or <td class='whatever'>.
& should be written & (because the & alone looks like the start of the & entity), etc.
Once you have converted the HTML, use the w3c validator to make sure it validates as strict XHTML.
If you have any errors, it will tell you about them so you can easily fix them and try again.