[jyl]

I'm not real good on these sorts of fixes - because I've had very few problems that need fixing - but the recommendations I read usually start with using Disk Utility to "repair" permissions on the hard drive. That seems to be a general first step for many Mac problems. I'm sure someone else will chime in though. If necessary, you can d/l iChat from here http://www.apple.com/support/downloads/ichatav.html

More on Disk Utility http://docs.info.apple.com/article.html?artnum=25751