Barney reveals that one of his "crimes", that he committed to one of the women of his past, was stealing her car and driving away from their camp in the woods, leaving her there alone. In an earlier episode "Arrivederci, Fiero" (s2e17) it is revealed that Barney can't drive a car and is, in fact, very afraid of the idea.
In the beginning of the episode, we see Barney's stalker from the back, as she is talking to Lily. She has curly, blonde hair. In a later episode, however, S. 03, E. 19: "Everything must go", the same shot is featured but clearly with a different girl who appears to have straightened, blonde hair.
The second girl Barney and Lily go to visit, Anna, couldn't have been the stalker. When the stalker is talking to Lily, she specifically says dating Barney was a terrible mistake. But Barney had told Anna he was Ted Mosby, which she still believes. Not only should she not be in the final four, she shouldn't be on the list at all.