bascily you just install vbulletin in the same folder as php nuke
then in the following files:
index.php
search.php
forumdisplay.php
and so on...
just don't put it in newthreads.php and newreply.php,because those files seem to allready contain header information.
put
if(!isset($mainfile)) { include("mainfile.php3"); }
include("config.php3");
include("header.php3");

below the first line,then put
include("footer.php3"); just before the last line

that's just doing it quickly....
if anyone else takes the time to put it in all vbulletin pages without errors please post here