Yes. Each User is required to register before they can make any posts or replies, allthough you are welcome to read any of the existing posts.
You are welcome and encouraged to update your information at anytime. All you need to do is click the Edit Info button, enter your UserId and Password and then you can updated your email address, homepage or any other part of your information.
Yes you are welcome to use HTML in your posts, but please make sure you close all of your tags properly. If this is misused the administrator has the authority to remove or edit your post as needed, or they can disable HTML in any particular forum.
To put a link in your post you just need to use the HTML tag for the link. So if you wanted to link to www.usatoday.com you would put <a href="http://www.usatoday.com">Here is a link to Usa Today</a>.
Cookies are used to mark read and unread messages and only last one session. When you first go into a board all messages that are unread since your last visit will be marked with a red dot. Once you leave that particular forum the cookies expire and will not show unread messages upon re-entering.
Yes. The entire source code of WWWThreads is available under the GNU GPL.