The code is built into the forum by default now, what you will need is the TinyMCE editor files installed on your server in order for the forum to use them.
If TinyMCE is in place already, then you should be able to select it as the editor in the Admin -> Host Settings -> Editing/Formatting Settings section.
If that doesn't help, then I suggest posting the version of the forum you are using so that someone can help appropriately.