My store had no idea what I was talking about when I first called them, so it was obvious that they didn't know about the misprint in the ad and didn't have a sign up or anything.
When I first talked to them, they didn't know what XP Media Center OS even was, and told me they had no computers with that installed. Fast forward to yesterday when their circular comes out with at least four computers listed with that OS.
So, after calling everyone in creation, I finally talked to someone who would give me what I wanted. I returned the BF HP bundle (no restocking fee) and got the HP a1230n instead. It was $799 after rebates, but I got $100 off for my trouble.
So I am finally satisfied with Circuit City's handling of this. Hope everyone else gets a satisfactory result from this fiasco! :)