ruspant, TheCorm, Justarius,
See my script in my previous post to accomodate some of those issues. The script will change the caption of the taskbar button when a new message is recieved.
However, the script is highly experimental and was only created as a test and proof of concept. As such it does not work 100% as you might expect (but it might be good enough):
"
CookieRevised's reply to Tabbed Chats - wrong contact"
Import the script and go to the Plus! icon menu in the onctact list or in a conversation and enable "Tabbed chat taskbar button changer".