Something like this should work:
when you click submit you load the same page but you also a control value, in this case called $control.
If $control is set then it will do everything needed to send the e-mail and then print a message. Else it will show the form
I know there probably is better ways to do it, but this is one solution:
<?php
if (isset(($HTTP_GET_VARS['control'])
{
Do everything to send e-mail here;
print("E-mail sent!");
exit;
}
<form>
<input>
</form>
I hope that gives somekind of help...
[Edit]
I went away a while so it took 2 hours to finish this reply, good it work for ya!!!
[/Edit]