Does anyone know how to make a image have rounded corners using a PHP script?
GD is great for image manipulation, but it would be much easier for you and much easier on your server if you used CSS.
Here's a great tutorial for some cool image effects using CSS:
http://www.webdesignerwall.com/tutorials/css-decorative-gallery/
For modern browsers, you can do it in pure CSS:
http://www.css3.info/preview/rounded-border/
A couple of other noteworthy ones:
http://www.spiffycorners.com/
http://www.html.it/articoli/niftycube/index.html