Last week I posted asking if anyone knew if Avid MC 6 would run on an early Mac Pro...
I have my answer.
The Mac Pro 1,1 and Mac Pro 2,1 have 64 bit Xeon processors and can run 64 bit apps, using more than 4GB of RAM just fine. They cannot, however, boot the 64 bit kernel in Snow Leopard and Lion, as the EFI firmware in these machines is 32 bit. (oddly, since windows does not use EFI, they can run the 64 bit version of Windows 7 in Boot Camp without issue).
I can report that although you get an error message when you install, noting that you are not running the 64 bit kernel, you can proceed with the installation....and it runs well...very well, actually. The app is running 64 bit, if you check in the Activity Monitor.
Mind you, the Mac Pro 2,1 I own is an 8 core 3.0 Ghz machine with 32 GB of RAM. The Mac Pro 1,1 is a Quad 2.66. , so the performance will not be as great, especially without maxing out the RAM (64 bit apps need lots of RAM). Also note, this configuration is not supported by Avid...but if you are not ready to retire your Mac Pro yet... MC 6 wih third party hardware is still an option for you. I have heard DX hardware will not run without the 64 bit kernel though, as the new kext is 64 bit only, but cannot confirm.
Right now I am loving MC 6 with my Decklink Studio card. I never thought I would see this.