The boot sequence from hard disk for every Windows system (XP, Vista and later) is the same:
1. MBR (first disk)
2. PBR on active (first disk)
3. OS loader/boot manager (ntldr / bootmgr) again on active (first disk)
[boot.ini eqivalent in Windows 7 is \Boot\BCD file]
MBR code can be NT5(XP) or NT6(Vista and later) - does not matter.
PBR code must correspond to OS - for XP -> NT5, for Windows 7 -> NT6
bootsect.exe has switches /nt52(XP) and /nt60(Vista and later)
No need to fix ntldr - it is already there, only boot.ini should be checked for correctness.
For fixing Win 7 boot files you can use bcdboot.exe.
(for example "bcdboot c:\windows" is all that is needed)
Best is you make every disk bootable and check if everything is OK when other disks are disconnected.
What you need - a Windows 7 Recovery CD (can be created in Windows 7).
On the recovery CD you have:
bootsect.exe (fix for MBR and PBR)
bcdboot for fixing bootmgr, BCD and other boot related files.
You can prepare boot.ini by putting default ARC path (multi(0)disk(0)rdisk(0)partition(1)\WINDOWS) for default and OS:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows XP" /fastdetect
assuming that partition1 (first primary partition is active). Later when all disks are put back in the system things will change ! Eventually boot.ini and BCD have to be adjusted again.
All "boot addresses" as you can see in boot.ini (ARC path) are "absolute":
first is disk position (0,1,2,....) then partition(1,2,3,....)
please note disk numbering starts from 0, partition numbering from 1 !
Note 1 (be prepared for the worst case):
You can always fix Windows 7 booting using the recovery CD and "StartUp Repair" option. Windows 7 must be the only disk attached when fixing for best result.
Sometimes you have to run StartUp Repair up to 3 times with rebooting after each run to achieve fixing.
For XP only boot.ini has to be adjusted for correct booting.
In your case only rdisk parameter has to be eventually fixed !
You can use ArcPaths utility
to display ARC Path to drive mapping.
In BCD the "boot addresses" (device parameter and osdrive parameter) are in the form "\Device\HarddiskVolumeN" (this is usually mapped to a drive letter like c:, d:, ...) where N is a number starting from 1.
You can use the utility WinObj from SysInternals to view drive to volume mapping.
I suggest before starting changes and fixings you get used (if you are not already) to all utilites (bootsect, bcdboot, WinObj).
For editing BCD you can use bcdedit or Visual BCD Editor.
Hope this helps.