Can't get z-index to stack things properly

Hi all,

I'm having a massive pain trying to get z-indexes to work on my blog.

http://www.ashrobbins.com

Basically I want the black div with the date in it on the left (.date_and_tags2) to display underneath the main white content area (#Wrap).

Can anybody see if there is a glaring issue here? I know that to use z-index, elements need to be positioned, and as far as I can tell they are.

Any help appreciated.

Thanks