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.

Why are there colons in the message when I try to post a follow-up?

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.

Can I put html tags anywhere in my posts?

No. You cannot use HTML tags in any field except body of the message. HTML in the Message part of your posting not allowed.