My advice - stay away from BD authoring for the time being. DVDA4 doesn't offer it, and there are no plans announced about whether it will ever or not. And while you can pick up the DVDit Pro HD upgrade for something like $200 - and no, it doesn't check to see if you've installed DVDit Pro first - however, the authoring it allows is very minimal - and IIRC, the only thing that will play the burned BD's are the PS3 and some third party players.

If you want to experiment with delivering HD content, pick up a copy of ULeads Movie Factory 6 ($80), get some regular -R blanks and have at it. With MPEG-2 encoding you can fit almost 23 minutes on a disk. If you go +R DL you can get up to 46 minutes. If Movie Factory ever supports VC-1 you might be able to push 2 hours of material onto the DVD.

AFAIK, all of the existing HD DVD set top players will happily play these disks. While Movie Factory only allows limited menu options, at least you do have the ability to create some decent looking animated menus.

At $200 for an HD DVD player, coupled with 30 cents for a SL DVD or a little more for a DL DVD, it certainly makes it an affordable way to deliver HD content (even if you do end up burning a few coasters). Depending on the project, you may even be able to factor in the price of the HD DVD player (for example, if this was a wedding project, I'd just add $200 onto my pricing so that when the B&G get the wedding DVD's, they also get a nice Toshiba HD DVD player to play them with).

Also, take a look at the huge discussion on this in the Vegas Video forum:
http://www.sonycreativesoftware.com/forums/ShowMessage.asp?MessageID=531655&Replies=89

--Scott