Thanks Alexis!
That seems to have done the trick:
http://en.tervuren.treekee.com/wiki/Main_Page
The version of MediaWiki is 1.7.1 and the change is slightly different, as
the line for the heading is a bit more complex, but the principle is
identical.
In MonoBook.php,
Before:
<h1 class="firstHeading"><?php
$this->data['displaytitle']!=""?$this->text('title'):$this->html('title')
?></h1>
After:
<?php if($this->haveData('title') != wfMsgForContent('mainpage')){
?>
<h1 class="firstHeading"><?php
$this->data['displaytitle']!=""?$this->text('title'):$this->html('title')
?></h1>
<?php } ?>