trying to import my Wordpress 2.9.2 content into my vBulletin CMS 4.0.2 using impex
 

I'm trying to import my Wordpress 2.9.2 content into my vBulletin CMS 4.0.2 using impex without success

I've set up impex and I'm confused as to what options I'm meant to be choosing. There seems to be two for Wordpress... wordpress_cms and wordpress (2.3.1). Which one do I choose as the system on the import screen? And what do I set the target export to? vBulletin 4.0.* or vBulletin CMS 4.0.* ?