auto image size adjustment

I got this hack from another thread, can't find the link, but I had it saved to my hard drive.

It adjusts all images that are posted using the [img] tag to a size of 400.

I was hoping somebody could help me tweak this hack.

in /forums/admin/function.php

find

PHP Code:

if($dobbimagecode and ($bbuserinfo[userid]==0 or $bbuserinfo[showimages])) {
      // do [ img]xxx[ /img]
      $bbcode = preg_replace("/(\[)(img)(])(\r\n)*([^\"".iif($allowdynimg,"","\?\&")."]*)(\[\/img\])/siU", "<img src=\"\\5\" 

border=\"0\" alt=\"\">", $bbcode);
    } 

replace with

PHP Code:

if($dobbimagecode and ($bbuserinfo[userid]==0 or $bbuserinfo[showimages])) {
      // do [ img]xxx[ /img]
              $thispic=explode('[img]',$bbcode);
        $thispic1=explode('[/img]',$thispic[1]);
        if ($thispic1[0] != ""){
        $size = GetImageSize("$thispic1[0]");
        }
        if ($size[0] >= 400){
             $bbcode = preg_replace("/(\[)(img)(])(\r\n)*([^\"".iif($allowdynimg,"","\?\&")."]*)(\[\/img\])/siU", "<img 

src=\"\\5\" border=\"0\" width=400 alt=\"\">", $bbcode);

           }else{
             $bbcode = preg_replace("/(\[)(img)(])(\r\n)*([^\"".iif($allowdynimg,"","\?\&")."]*)(\[\/img\])/siU", "<img 

src=\"\\5\" border=\"0\" alt=\"\">", $bbcode);

           }

    } 

NOTE: I had to put a space in the image tags "[ img]xxx[ /img]"

The part that I would like help with is getting is so that the image automatically makes itself clickable to see the full version. Can somebody please help me out with this?

I was also wondering if something like this could also be implemented to the attach feature, so that if somebody attaches an image into a post it does the same thing, where it's small and clickable for the larger version?

If somebody could please help me, I would greatly appreciate it.

Thanks for any help you can offer.