Expert1510, if you are meaning in an actual forum post from what I have experienced it is not possible using the uCoz $CHAT_BOX$ code but it will work if you copy the HTML/Script of the chatbox to the post with HTML enabled.
The script as in meaning the source code of the tag board not the designs.
Hope this helps,
Web Applications Developer Been here for 7 years and counting. Visit me at alexmoloney.me.