Theme a view of one content type with node references to another I'm attempting to theme a view containing of content type 'Activity' which includes Node References to a second content type 'Category'. 

When using the views-view-list template it appears I cannot access or the fields which are included through Node References.

Any help would be appreciated.
What you need to do is add a view relationship (in Views 2 and Views 3) that uses your node_reference field to create the relationship. This will make these fields available to your view.

Thats the quick answer, this video explains it better:

http://gotdrupal.com/videos/drupal-views-relationships