Here's the URL for the press release I referenced.
I know for certain that ESPN-HD's native format is 720p
Ditto for ABC and Fox. HD-Net, CBS and NBC are in 1080i.
http://sports.espn.go.com/sports/tvlistings/espnhd/espnHDStory?id=1802691
Thanks for the link, I need to figure out why it's dsiplaying 1080i.