[tubedogg]

I was about to answer 'not without hacking', then I realized that's probably why you're here.

Anyway, find

PHP Code:

if ($action=="finduser") {
  // get allowable forums:
    $forumsql=getallforumsql(); 


and replace it with

PHP Code:

if ($action=="finduser") {
  // get allowable forums:
  if ($forumid) {
      $forumsql = "forumid='forumid'";
  } else {
      $forumsql=getallforumsql();
  } 


Then add &forumid=$post[forumid] to the search link for the user. I'm not sure if $post[forumid] will do anything by itself...you may need to add some code to functions.php. You might also try $thread[forumid] before you add anything tho.