Spørgsmål vedr. billedgalleri

Når man klikker på billedet skal det poppe op i et nyt vindue. Hvordan gør man det? Her er sourcekoden:

<?
//----  Settings Start ---\\
// Image Information
$imageWidth=130;
$imageHeight=107;

// Table Layout
$rows=100;
$cols=4;

//Image path
$libery="billeder/dorautomatik/"; // remember to finish with /

// Settings Stop----------//

$viewNum=$cols*$rows;
if(!$firstImage){ // so it works if you just enter default.php and show the pictures without having to define the variables in the path
        $firstImage=1;
}
function getImages($firstImage){
    global $viewNum, $imageWidth, $imageHeight,$cols,$libery;  //insures that the function gets the variables
    $handle=opendir($libery); //opens directory
    while($file=readdir($handle)){ // reads the directory
        $extension=substr($file,-4); // gets the extension of the files
        if(($extension == ".jpg") || ($extension == ".gif") || ($extension == ".png") ){ // checks for image files
            $all[]=$file;  //adds positive results to the archive
        }
    }
    $colscounter=0; // variable that controls the tablebuilding system below
    $firstImage--; // variable that insures that the first image is being showed. Case: It looks best if the links begins with 1 but the array begins with 0
    if(isset($all)){  // if array is set build the table
        print "<table>";
        for($i=$firstImage; $i < $firstImage+$viewNum; $i++){
            if($all[$i]){ // checks for rinning dry of imges
                if($i==$firstImage + $colscounter*$cols){ // if true: new row
                    $colscounter++;
                    print "<tr>";
                } // add the image
                print "<td><a href='".$libery."".$all[$i]."'><img src='".$libery."".$all[$i]."' border='1' width='$imageWidth' height='$imageHeight' alt='Click to Enlarge'></a></td>";
            }
            else{ // stop if no more images
                break;
            }
        }
        print "</table><br>";
        $num=count($all);  //number of pictures in actual libery
        makeList($num); // function to make the links list
    }
    else{
        print "Der var desværre ingen billeder i dette bibliotek<br><a href='java script:history.back()'>Go Back</a>";
    }
}
function makeList($num){
    global $libery, $firstImage, $viewNum; //insures that the function gets the variables
    $numLinks = $num / $viewNum; // finds the number og links to be maked
    for($a=0; $a < $numLinks;$a++){
            $start=$a*$viewNum+1;  //adds 1 because then the links begins with ex. number 1-10 and 11-20 instead of 0-10 and 10-20
            $finish=$a*$viewNum+$viewNum;
            if($finish>$num){ // insures that the final link returns the right amount of pictures instead of to much
                $finish=$num;
            }
        if(($firstImage >= $start) && ($firstImage < $a * $viewNum+$viewNum)){ // if true: makes no link because you already are on the page
            print "$start - $finish</a>&nbsp;&nbsp;";
        }
        else{ // makes the link
            print "<a href='index.php?side=billeder/dorautomatik?libery=$libery&firstImage=$start'>$start - $finish</a>&nbsp;&nbsp;";
        }
    }
}
?>
<div align="center">
<?
getImages($firstImage);
?>
</div>