Error with getElementByID using XML

I've loaded an XML doc of options and I'm trying to get to a specific node using its ID.

I'm stuck on the line:

set el = getElementByID(strParent)

VB says the Object doesn't support this property or method (?!).

(I set the ID attribute in the DTD, still have the same problem.)

I've set up a test page at:

URL
(code is shown)

Any help would be appreciated!!!

Thanks,

Heidi