You can either set up an instant redirect to your forums (So you don't have to have a page on mydomain.com that says "Please stand by, you will be redirected to the forums in a few seconds" with either HTML or PHP.
HTML:
Create a index.html file
Here's the code.
Code:
<HTML>
<HEAD>
<META HTTP-EQUIV="refresh" CONTENT="0;URL=mydomain.com">
</HEAD>
<BODY>
</BODY>
</HTML>
Copy that code into the HTML file, but change mydomain.com to yourdomain.com/forum.
If you'd like to do it with PHP (your preference), here is the code.
Create an index.php file
Code;
Code:
<?php
header( 'Location: mydomain.com/forum' ) ;
?>
Change mydomain.com/forum to your domain.
If you would like it to redirect them in a few seconds.. lets say 5.. you would change the 0 to 5 seconds in the HTML code
Good luck