Can I put html tags anywhere in my posts?
No. You can not use HTML tags in any field except body of the message. The maintainer of the script has the option of allowing or disallowing any HTML in the Message part of your posting. If they disallow it, the script will just throw out everything in <>'s. If they allow it, your html markup will appear in the posting. It can't hurt to try.
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.
Why didn't my post show up?
Your post most likely did not show up, because your browser did not reload the page, it simply pulled it out of cache. Please reload your browser and it should then appear.