index.php?act=test&cat=5

How is that done, I know how to to the act bit:

[code:1:7a6c10e548]
<?
switch($_GET['act']){
case '1':

?>
This is act 1
<?

break;
default:

?>
Default
<?
}
[/code:1:7a6c10e548]

But how do you add categories?