Unable to boot OS x


I have MacPro Quad Intel with Four Hard Disks.
Disk 0 has 200MB EFI System Partition and 232Gb Macintosh HD with Leopard installed.
Disk 1 has 200MB Bootcamp , 120G NTFS with Vista Ultimate and two Logical NTFS partitions for data.
Disk 2 has 200MB Bootcamp, 150G Mac Time Machine and 32G NTFS with XP MCE installed.
Disk 3 is as yet unused.
Mac Boot menu ( accessed with ALT key) is set to Windows default.
This brings up the Vista Boot loader with choice of Vista or XP.
All efforts to add OS X to the Vista bootloader and so avoid necessity to use ALT key for MAC, have failed
Usual error is corrupt or missing nst_mac_mbr.
Any help appreciated.
This would be due to the bootcamp. If i am not mistaken this has everything to do with how Mac's boot up and the bootcamp which only allows for booting between OS X and 1 copy of Windows. You can read the documentation:

Mac OS X - NeoSmart Technologies Wiki

But Mahmoud will have to give you a definate answer. But i am sure this has something to do with bootcamp.