>>>>> "John" == John  <john-xsl-list@xxxxxxxx> writes:

    John> I have an XML file on a web server which references an XSL
    John> with code as follows:

    John> <?xml-stylesheet type="text/xsl" href="somefile.xsl"?>

    John> When IE or Firefox requests this XML file, the browser
    John> detects the stylesheet reference and applies it to the XML
    John> to transform it into HTML.  This works great, but what if I
    John> want to let the user choose from multiple XSL files which
    John> can be applied to the same XML? 

You have to code alternate="yes" and title="some descriptive choice-name" 
on the xml-stylesheet PI.

And least, that's how it's supposed to work - I haven't tried it.
-- 
Colin Paul Adams
Preston Lancashire