Another idea (to be tested).
Let's set explicitly (and as *recommended*):
the 100 mb partition as ID 0x27, keeping it Active, there would be NO practical difference for Windows 7:
What would do Windows XP setup?
It won't see it, but would it "force" or "require" the "W: thing" to be active? (or refuse to install if not, not knowing where to put NTLDR, etc.?)
And how would it behave for the partition "in the middle" (the largish one hosting Windows 7)?
Most probably it will assign to that partition the C:\ drive letter, so a migrate.inf would be needed anyway.
If we pre-add to the "W:\ thing" a BOOT.INI with a grldr entry, grldr and a menu.lst pointing to the BOOTMGR on the Windows 7 "system" partition, the XP setup should "keep it", adding to it the actual arcpath to the new install, and you could (once) boot through grub4dos to the Windows 7 and from it "fix the booting" (without needing booting form "external", i.e. (this might be interesting as a side note), what if the 100 Mb partition, set as either 0x07 or 0x27, is made active after (and a copy of NTLDR/NTDETECT.COM and BOOT.INI is made from the ones the setup placed on the (at the time of install) active "W: thing" (which should have gotten according to your experiment the C:\ because it was active at the time of install)?
Would the Windows 7 bcdboot (or similar) command add *automagically* the XP as dual boot to the \boot\BCD?
Or we still need to edit it manually with BCDedit or similar?
Edited by jaclaz, Today, 02:09 PM.