In a reply to myself, I found the following:
in chat/index.php
Line 48:
Code:
$nonalnum = ereg_replace("[^ [:alnum:]]", "", $bbuserinfo[username]);
Change to say the following:
Code:
$nonalnum = preg_replace("/^(\d.*)/","_\$1", $bbuserinfo[username]);
That should cause the forum to add an underscore to the front of the nickname if it begins with a digit, and leave it unmolested if it does not.