createNSResolver IE7

I was pleased to find out that IE7 now has native XmlHttpRequest()
support.  however, it doesn't (perhaps obviously, perhaps not) seem to
support all of the functions Mozilla supports, including
createNSResolver.

My AJAX code splits between browsers that can support XmlHttpRequest
natively (FF, Opera, Safari), and those that need ActiveX (IE 6).  If
the browser supports XmlHttpRequest natively, then my code assumes it
also supports a bunch of other functions as well.  Perhaps this is just
bad design, but IE7 bombs on createNSResolver.  Simply forcing my code
to have IE7 flow through the ActiveX method solves the issue for now,
but I'd like to know if IE7 has some kind of analogous function to
createNSResolver.

Any help is appreciated.

Thanks,
Ben