No. You can not use HTML tags in any field except body of the message.
Colons appear in the message dialog box when you followup up on a message. Those lines are quoting the previous document. You can delete them if you want. Otherwise, put your text below the lines you are responding to.
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. If this bugs you, in Netscape go into Edit/ Preferences/ Advanced/ (click the plus) Cache/ and select that the cache is compared to the network everytime.
The scripts are written in Perl and created by Matt Wright. They are free to anyone who wishes to use them and you can get them as well as other scripts at: http://worldwidemart.com/scripts/. Enjoy!