well im not much of an on-site chatter, but i know the major pain a flash platform can be in the ass.... It's a strange platform of choise to say the least. mIRC sounds like a much more proven platform. As you stated before, an AJAX chatbox would be a good choise also, but it'd require some resources to program ofcourse. Resources 'rosity might not be willing to dedicate? (if they did they've either not thought enough of the possibilities or didnt realize the potential)
I'm not much of an on-site chatter myself, but you cant get a much better deal then an IRC channel...

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