Cannot display custom field values in admin post listing

Hi there

After creating a custom post type, all's working except I would like to display one of the custom fields in the admin view listing for the custom post type. I can get the column heading to show, however the field values themselves do not show in the listing. Any thoughts please?

I have a screenshot to help explain better.

http://www.bergs.net/wpmudev.png

Thanks.
Cheers
Warwick