So one more time about mailing. In practice we often need to send mail in appropriate format. There are a lot of articles about this problem, especially with enormous quantity of code. As for me I tried to use it but in most cases all this code didn't work for me. My mail problem has to be solved in a short time that's why I decided to use module. I've tried a lot of them, but only mime mail http://drupal.org/project/mimemail . Its usage is very simple: you should turn it on and chose html format inside dropdown list which is situated on mime mail configuration page.
So i hope my information will be usefull for you.