well, i have a mac G4 and i have no problems to chat, i also have no "send" button, i just hit the enter key and my message is in... make sure to use IE4 or higher to chat, the best is, if you have'nt already, to install both programs (IE and MOZILLA) and try the other one if any problems occur. maybe you do already so and if the problem still occurs i have no idea... just my experience
Ray