Humpty,
You've gotta uncheck all of your old HD before it will even let you order the new HD.
If you were on the old $62 package, its new edition will give you 4 HD packs for 10 bucks. Make sure that if you do this you also select the separate item "HD alternate feeds" because you get the US Networks East HD feeds if you live in the west or West HD feeds if you live in the east for free if you check this and have already selected 4 HD theme packs. By the way, you get all of the candian networks and some canadian specialty channels in HD for free under the new structure. One difference between old and new is that once the preview ends, the old subscribers won't have access to NG HD or Showcase HD unless they switch over to theme packs. Right now, with HD packs are kinda small (2 or 3 channels each), and there are 5 of them, so you'll lose 2 or 3 channels (I opted to go without Rush HD and Rogers Sportsnet HD).