Advanced Thumbnails

Hi all.

I have created a custom field for my posts, which is usually a specifically sized image, but can also include flash video or embedded audio players.

What i would like to do is, use this image in an archive list as a thumbnail. I need to

1. Check to make sure it is an image.
2. If it is an image, resize to 150px square
3. If it is not an image, grab a default thumbnail.
4. From here i will style it with CSS.

I tried using Justin Tadlocks “get the image” plugin, but it would pull the content whether it was an image or not.

my site is here: http://nerdynothings.com

I want to take the home page images and reuse on the category archive page, only as thumbs.

any help would be appreciated.