DOH!
Nevermind. I found it two minutes after posting this (I looked for half an hour before resorting to the post!). Must not have had enough coffee yet.
For anyone else who wants to make this mod, here's the code you look for:
In com.php:
<table width="90%" border="0" cellspacing="0" align="center">
<tr>
<td>
<hr size="1"><DIV class=comment>$com[name]:<br>
$com[comments]</div>
</td>
</tr>
</table>
Change it to:
<table width="90%" border="0" cellspacing="0" align="center">
<tr>
<td>
<hr size="1"><DIV class=comment>$com[name] says:<br>
$com[comments]</div>
</td>
</tr>
</table>
I made this mod because it clarifies that it's a response from [name] rather than a comment addressed to [name].
Hope somebody finds this useful!