Hey all!
Since this can be usefull for someone here it is
I can confirm I sucessfully booted DOS from CD on MacPro. I was playing along with GPU firmware and I needed DOS. So after using spare PC's for the job I thought hey if XP installer works, why shouldn't plane old DOS. Well and it did 
So if you need DOS for DVD drive firmware flashing, GPU bios flash experiments (like dumping original MacPro X1900XT flash etc.
you can do it!
HOWTO for DOS boot CD:
- Make a DOS bootable floppy or usb stick (if you need more stuff use USB, I did) (www.bootdisk.com, I used XP Startup disk floppy image)
- Put on it everything you need (atiflash, bios image...)
- Burn bootable CD with Nero (select floppy/usb as source for boot sector)
HOW to make bootable USB (since MacPro has no floppy):
- Get a bootdisk image (www.bootdisk.com) and extract it to folder
- Download HP Drive Key USB Boot Utility http://h18000.www1.hp.com/support/files/serveroptions/us/locate/69_6073.html
- Use it and point it to your USB key and extracted boot disk image
When CD is made it will look empty! Don't worry that's normal since bootsector stuff is not visible in explorer/finder...
Since this can be usefull for someone here it is
So if you need DOS for DVD drive firmware flashing, GPU bios flash experiments (like dumping original MacPro X1900XT flash etc.
HOWTO for DOS boot CD:
- Make a DOS bootable floppy or usb stick (if you need more stuff use USB, I did) (www.bootdisk.com, I used XP Startup disk floppy image)
- Put on it everything you need (atiflash, bios image...)
- Burn bootable CD with Nero (select floppy/usb as source for boot sector)
HOW to make bootable USB (since MacPro has no floppy):
- Get a bootdisk image (www.bootdisk.com) and extract it to folder
- Download HP Drive Key USB Boot Utility http://h18000.www1.hp.com/support/files/serveroptions/us/locate/69_6073.html
- Use it and point it to your USB key and extracted boot disk image
When CD is made it will look empty! Don't worry that's normal since bootsector stuff is not visible in explorer/finder...