This was a tough one, but I managed to prove my theory that XP can be
installed last and still added to the bootloader. It was simple to do
with two cmd lines, but damn hard to find and figure out.

My
first problem getting Vista off of XP (I didn't want to use
VistaBootPro in solving this puzzle) so I could add XP after the Vista
install without any traces of it left from the bootloader. I could have
reinstalled XP and cleaned it up, but a little research revealed a much
quicker way with bootsect.exe. The syntax is:

E:\boot\bootsect.exe
/nt52 ALL /force (E is your Vista install DVD). The ALL is all systems
older than Vista. Ignore the errors from your USB drives. It basically
switches XP from Vista BOOTMGR to the older NTLDR.

Having a
cleaned up XP I installed Vista on my second freshly formated drive
with the XP drive disconnected. This of course was to keep Vista from
besmirching it with the bootloader. Install went fine and after
reconnecting XP, I could boot either OS by selecting the appropriate
drive in BIOS.

However this isn't what I was after; I still
needed to get a bootloader onto XP somehow AFTER installing Vista. I
couldn't get Vista install to do the job without doing a clean install
on the old Vista, and that would be cheating as I would make XP the
previous system. An upgrade would only upgrade XP and not Vista.

I
was about to give up when the thoughs of the "bootsect.exe" was
whispering to me about something on the screen when I used it,
something about "restoraton tool." Whoa! I quickly opend a CMD and
typed:
E:\boot\bootsect.exe /? and got the following:
bootsect {/help|/nt60|/nt52} {SYS|ALL|:} [/force]Boot sector restoration tool

Bootsect.exe updates the master boot code for hard disk partitions in order to
switch between BOOTMGR and NTLDR. You can use this tool to restore the boot
sector on your computer.

Run "bootsect /help" for detailed usage instructions.
Wow!
There is was!!! Now I see I need /help instead of /?. Which I did, and
came up with detailed instructions. Now by this time I copies the
bootsect.exe to my root dir where it was handy. Why was this such a
secret. Here is what I used to install the boot loader, two simple
lines:

C:\>bootsect.exe /nt52 C: /force (for XP just to be sure it is NTLDR)
C:\>bootsect.exe /nt60 D: /force (to fix Vista)

For reference here is the help file displayed for bootsect.exe, the boot sector restoration tool.


CODE
C:\>f:\boot\bootsect.exe /help



bootsect {/help|/nt60|/nt52} {SYS|ALL|:} [/force]



Boot sector restoration tool



Bootsect.exe updates the master boot code for hard disk partitions in order to

switch between BOOTMGR and NTLDR. You can use this tool to restore the boot

sector on your computer.



/help Displays these usage instructions.



/nt52 Applies the master boot code that is compatible with NTLDR to SYS,

ALL, or . The operating system installed on SYS, ALL, or

must be older than Windows Vista.



/nt60 Applies the master boot code that is compatible with BOOTMGR to SYS,

ALL, or . The operating system installed on SYS, ALL, or

must be Windows Vista or WindowsServer "Longhorn".



SYS Updates the master boot code on the system partition used to boot

Windows.



ALL Updates the master boot code on all partitions. ALL does not

necessarily update the boot code for each volume. Instead, this

option updates the boot code on volumes that could be used as Windows

boot volumes, which excludes any dynamic volumes that are not

connected with an underlying disk partition. This restriction is

present because boot code must be located at the beginning of a disk

partition.



Updates the master boot code on the volume associated with this

drive letter. Boot code will not be updated if either 1)

is not associated with a volume or 2) is

associated with a volume not connected to an underlying disk

partition.



/force Forcibly dismounts the volume(s) during the boot code update. You

should use this option with caution.



If Bootsect.exe cannot gain exclusive volume access then the file

system may overwrite the boot code before the next reboot.

Bootsect.exe always attempts to lock and dismount the volume before

each update. When /force is specified, a forced dismount is attempted

if the initial lock attempt fails. A lock can fail, for example, if

files on the target volume are currently opened by other programs.



When successful, a forced dismount allows exclusive volume access and

a reliable boot code update even though the initial lock failed. At

the same time, a forced dismount invalidates all open handles to files

on the target volume. This could result in unexpected behavior from

the programs that opened these files. Therefore, you should use this

option with caution.



Example:



To apply the master boot code that is compatible with NTLDR to the volume

labeled E:, use the following command:



bootsect /nt52 E:



C:\>

Apparently the /nt60 must also cause
bootsect.exe to modify the BCDedit. Damn why does Microsoft hide this
wonderful stuff. Well probably because using the /force can be
dangerous too.