Worried about people posting malicious code in your comments, but still want the functionality of HTML enabled comments?? You might want to check out the MT Sanitize Plugin. It "allows you to clean HTML and other markup that might exist in an comment entry." It will let you list the acceptable HTML that you allow in your comments, and then it filters out the rest. Smart!
To run MT Plugins, you need to be using MT2.21 or higher.