I'm, using Firefox, IE6, and Opera. Although nothing seems to work in opera so I will ignore it. In FireFox and IE6, I can see the HTML editor just fine in these forums. In our own though, nothing. Had some help from a guy at College who manages the college moodle. He independently tested our site and confirmed that although he can get the HTML editor fine in the college Moodle, he was also unable to get it in our Moodle.
Hope this helps.