In your VB3.php file I am assuming your using or whichever file your using do this
Find this line or depending on your integration file one something like it.
$regtext = " | <a href=\"{$Globals['vbulletin']}/register.php?action=signup\">{$Globals['pp_lang']['register']}</a>";
change to this
$regtext = " | <a href=\"{$Globals['homeurl']}/member/signup.php\">{$Globals['pp_lang']['register']}</a>";
If your a member is under the forums directory then it can be this
$regtext = " | <a href=\"{$Globals['vbulletin']}/member/signup.php\">{$Globals['pp_lang']['register']}</a>";