Did Bertrand Russell read and analyse Anselm's Ontological Argument and if so did he have anything positive to say about it?
He did. Read the relevant chapter of his "History of Philosophy". I don't have it with me, but I seem to recall that his criticism of the argument centers around the fact that Anselm treats existence was a (first-order) predicate. Russell thinks this is nonsense.
Russell's wrong. There are perfectly cogent ways of representing existence as first-order, but that's a different discussion.