[Logician]

let's see if this works:

edit register.php, find:

PHP Code:

eval("standarderror(\"".gettemplate("error_activatedthanks")."\");"); 


Replace it as:

PHP Code:

$url="forumdisplay.php?s=$session[sessionhash]&forumid=XX";
eval("standardredirect(\"".gettemplate("error_activatedthanks")."\",\"\$url\");"); 


Replace XX with your forumid..

Or if you want to redirect to a thread that line must be:
$url="showthread.php?s=$session[sessionhash]&threadid=XX";