Emma, I know this question was asked a very long time ago, but I'm answering here just in case anyone else comes across this post.
It looks like the original document on Auto-Page Tagging is dead and the new link posted by Eloqua support is for standard Page Tagging, not Auto Page Tagging. I believe this is the official Auto Page Tagging Document: Page Tagging: Creating Auto Tagging Rules
One step that is missing from that documentation, and this is something that tripped me up, is that after you have the Auto Page Tagging rule built, you actually need to run the rule in order for all the page tags to be generated. To run the rule, do the following:
-Save the Auto Page Tagging Rule by clicking "save" in the bottom right-hand corner.
-In the top-left of the screen, click the "Page Tagging" drop-down menu, then select "Mange Auto Page Tagging Rules" from the list
-Now you will see a list of the rule(s) you have created
-Click the plus sign beside the rule to expand the details about the rule
-To the left of the name of the rule there is a little drop-down button. Click it.
-Then select "Run Rule"
-Click "yes" in the confirmation box
Note: If you add criteria to an Auto Page Tagging rule you will need to re-run the rule