I thought digg was a blog, not phpnuke or any other cms but I could be wrong :?

Maybe try looking at blog software such as Wordpress or b2evolution.

Lastly, are you sure that when you submit a comment at digg, it automatically gets added to the sites content? I find it hard to believe a site that big would take those kinds of chances. It seems more likely to me that your submission would go into a queue to be approved by a staff member.