Script for re-sizing images in Photoshop CS2

I have a script for Photoshop CS2 which re-sizes an image.

Some are portrait-oriented (taller than they are wide) and some landscape-oriented (vice versa), each of them are re-sized to fit within a 500 x 500 pixel square. If the image is portrait-oriented, then I need to resize proportionally, setting the height to 500 pixels. If it's landscape-oriented, then I should resize proportionally with a 500 pixel width, instead of height.

The script I have does this but the canvas size isn't adjusted. So once the script for the above has run I want additional scrip that will adjust the canvas size to 500 x 500 pixels.