I haven't downloaded 5.4.3 yet, so this applies to 5.4.2 (but you should be able to figure it out, esp. since this script may not be affected by the upgrade). Here's the hack:
You must edit main.inc.php file at about line 138, where it says:
echo "<TITLE>$inputTitle - $lang[POWERED_BY] WWWThreads PHP</TITLE></HEAD><BODY>";
There are several ways to do this--here's the simplest and most direct:
Change the above to this:
echo "<TITLE>$inputTitle</TITLE></HEAD><BODY>";
...which will simply give you the title of the page, so that--for instance--on the Main Index page of the forum, the title would read "Viewing list of forums." This method won't necessitate editing any of the asssociated language files, which is what $lang[POWERED_BY] references.
Here's another variation:
echo "<TITLE>$inputTitle - Your Site Name</TITLE></HEAD><BODY>";
Make sense?