I'm very sorry, but I forgot something that is useful. First, I forgot to say that to make html emails it's better to use some specific class that allow to do it easily and simply. The standard mail function works right with plain text emails but it's not so good for more sophisticated usages. I suggest to use <a href='
http://webscripts.softpedia.com/script/Email-Systems/Template-Mailer--38063.html'>TemplateMailer class</a> (I'm not sure how I can insert a clickable link, so I don't know if this works). In the zip archive you can find the class itself and a demo file. I've used it to send html mails to registered users of a site and it works very fine, it's free and very flexible. Take a look and if you encounter some problem I'll try to find my old code to help you - but I think you will use it without any problem.
Bye