Ok, I’ve got it to work now. The problem was that I was writing the IFrame as an emtpy tag – that is, something like <iframe src=”foo”/>, rather than using an opening and closing tag , such as <iframe src=”bar”></iframe>. It looks like for some reason the WP html parsing wasn’t able to handle it – must have been treating it as an unclosed element, and so it was gobbling up the whole page.
Malcolm