Sadly iChat does'nt support profiles but if i remeber right some of the earlier builds of Tiger (Hint, Hint) had it implemented. As for now I am throughly impressed with AdiumX as it uses MUCH less system resources. but lacks AV capability :-(
I've seen this thread a million times. These guys are right, iChat AV doesn't support profiles yet. I'm almost positive that Tiger will change that. For the time being, there's a nice little app called iProfile that takes care of the job.
Or, as previously mentioned, you could download AdiumX.