Hi Ben,

That ought to be a pretty straightforward thing to hook up.
A couple of things to try:

First off, if you aren't using the 'in-testing' version at

http://www.projectpluto.com/new.htm

then I'd recommend doing so. It does include some bug fixes,
and mysterious behavior of this sort often vanishes with the use
of the current software.

You may also find that using the ASCOM driver for this scope
works. (Though in truth, I can think of no good reason why Guide
would fail to recognize any Celestron scope.)

Do you get any error message(s) that might provide a clue as
to where the stumbling block is?

-- Bill