Dear Kongkang thank you for the quick reply.
I am using timthumb.php to call the thumbnails on my front page. The script looks for a custom field named thumb with the url of the image. If it exists then it generates and displays the thumbnail.
I want to use the same custom field to display the same thumbnails on the category page (https://img707.imageshack.us/img707/5465/mrama.jpg)
How this extra info affects your solution?