Smileys

I'm running a php3/mysql driven site
I update my site with an addnews form and that is working ok...
but now i wanted to try to include URL images in my newspostings...
so i add a form of text in which i just include basic : ) stuff and when they are displayed onscreen the : ) is automatically converted to <img src="images/smiley.gif"> or something similar...
how can i do that ?

The King says: use preg_replace, getImagesize.

$image = "images/smiley.gif";
$imagesize = getImagesize ( $image );
$tag = sprintf("<img src="%s" %s", $image, $imagesize[3] );
$text = preg_replace("/ URL/", $image, $text);