After some further messing around, I suspect ES is a lost cause on Leopard due to all the changes in how 10.5 uses Services, and since ES hasn't been developed in ages (still PPC!!)... But thanks, zacw for working on this. :)

More details:
When I try to typset an equation in Adium, Adium pauses for a while and then reports back to me that it could not typeset an equation because ES is not responding (and I have to force quite ES).

Is there any way to get this working with LaTeXIt instead since ES hasn't been developed in AGES?

I can't get this working (up to date on Adium v1.2.5), I have Equation Service installed and configured, however when I type test LaTeX into Adium, ES launches but nothing happens (I receive the message back as plaintext not TeX).

I am on Leopard (up to date with patches), so I'm not sure if it's a problem with ES and Leopard in general, with Adium and ES and Leopard, or just my setup...