<p>More specifically I am trying to make the mailto component show within my template; the same way as an article does. </p>

<p>By default the mailto component opens in a new window. So far I changed the code so it opens on the same window, but that way the whole template is gone.</p>

<p>Any suggestions?</p>

I'm afraid I can't entirely follow your question - do you want to have a sign up form for membership or email notifications shown as an article? If so, then the easiest way is to install 'm2c' - the 'module to component' component. Then you can put any module (ie the sign up box) in the centre content area.
The m2c component can be found here:
http://joomla.focalizaisso.com.br/en/componentes/index.php