It took me a few reads to finally realize what you meant by HD-DVD.
Do NOT buy those discs. The format has been discontinued and you won't be able to get all the episodes in that format. They only did season one.
Since HD-DVD as a format DIED Paramount stopped producing in that format, and the only high def discs that will have the whole series will be the blu-ray ones.
Also, if I understand right, the b-r discs will have both versions of the episodes (the original versions and the CGI remastered versions). If I'm wrong on that, someone correct me.
Of course, I don't know if there are SD versions on the blu-ray discs that'll play in a regular DVD player.