Can I put html tags anywhere in my posts?
Yes, you can.
Why are there colons in the message when I try to post a followup?
Colons appear in the message dialog box when you respond to a message as indication 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.