Rule to add taxonomy term

Hi all, if someone could point me in the right direction I'd be very grateful.

I am setting up a simple rule to add a taxonomy term when a new node is created. The term name will be the title of the node.

I have added the title of the node to a new string variable, however when I go to add the taxonomy term action its still unavailable - "Assign a term to content - Unavailable argument: Taxonomy term". How do pass the argument?

I'm using drupal 6.13 and rules 6.x-1.0

Thanks

John