Is there another app on the Mac that will author HD DVD in the same fashion as DVD Studio Pro. In others words, I want to get my HD footage onto a regular DVD and have Apple DVD Player play it back - any solutions?

Haven't seen anything else yet. I'll keep looking though.

Pinnacle makes a PC product that you might be able to run if you have an Intel Mac and something like Parallels virualization.

http://www.pinnaclesys.com/PublicSite/us/Products/Consumer+Products/Home+Video/Studio+Family/HD+DVD+Authoring+pack+Documents/Technical+Specifications/HD+DVD+Authoring+tech+specs.htm

There is an article at www.kenstone.net that talks about this.
http://www.kenstone.net/fcp_homepage/hd_dvds_on_sd_dvds_young.html

To get DVDSP to burn an HD DVD that plays in DVD Player as well as a Toshiba set top player, you need to encode your video into MPEG2 HD and your audio into AIFF.
H.264 and AC3 do not work (yet?) Menus do not work either. Chapter stops work fine.
The down side to MPEG2 HD / AIFF is the bandwidth. You can only get about 30 mins. on a standard 4.7GB disc. The up side: it looks great.

My old G4 dual 1GHZ is apparently too slow. Discs play fine on my G5.

The problems with HD DVD's and playing in the Toshiba and Xbox players is completely fixed. Menu's work as well. As far as I know though, DVD Studio Pro is the only App on Mac's that burn HD DVD's. Hopefully at NAB, we will get full Blu lazer support as well.

Fred: Does that means that it's possible to 'manually' create a HD DVD that plays on Apple's DVD player, without the use of DVD Studio?

I am not aware of any other Mac application that creates HD DVD.