You can not put scripts or any kind of HTML anywhere. You will have to convert them into BBCode. You can do this by going to the Posting tab of your Advanced Admin Panel.
Once you've made a Custom BBCode for it. You can put that in Topics and Posts, but not on the Board Index as Custom BBCodes have been disabled on there. Forum Descriptions, Welcomes Message, Chatbox all do not support Custom BBCodes. This was because there were too many exploitations possible which caused a security threat.
If you need help with creating your BBCode, please post your HTML Code in here and we will see if we can help you
SEO Link Building |Link Building Company