[Znaper]

Search for this code in your index.php:

if ($newpm['messages']==0) {
    $lightbulb='off';
  } else {
    $lightbulb='on';
  }

and replace it with this:

if ($newpm['messages']==0) {
    $pmsound = "";
    $lightbulb='off';
  } else {
    $pmsound = "<bgsound src=\"gotmail.wav\" border=0>";	
    $lightbulb='on';
  }

Now you can use the $pmsound variable in your forumhome template.
Replace the gotmail.wav with your soundfilename!