No. HTML tags can only be used in the body of your message.
Why are there colons in the message when I try to post a followup?
Colons appear in the message dialog box when you try to followup up on a message to indicate that those lines are quoting the previous document. Just like quoting text in replies to email messages.
Your post most likely did not show up, because your browser did not reload the page, it simply pulled it out of cache. Please click the reload button on your browser and it should then appear.
It just won't work for me - who's going to help?
Sorry you're having trouble. Send a message to mark@his-computer.com and he'll do his best to help. Please give as much info as you can including the date and time and the browser software and Internet provider you're using.