Nothing is impossible.
If you´re using RC1 open Templates/default/ajax_chat_body.tpl
in case of .27 open templates/your_theme/ajax_chat_body.tpl
Using RC1 opened Templates/default/ajax_chat_body.tpl in string:
"<table class="forumline" width="40%" cellspacing="0" cellpadding="0">" where "40%" was changed on 25%
No result