http://developer.aim.com/aimccMain.jsp
AOL released a SDK for developing your own AIM client, and it also has PPC stuff within the SDK. I know that there is an ARM AIM client that'll run on 720s, but it's really pretty crappy. Very limited, almost impossible to switch between "windows" with the stupid little button on the top when you use your finger....really needs some work.
I wonder how well the PPC stuff can be moved to HPC
(through some "tweeking"
and having it built for HPC as best it can.