OK, succeeded -- finally !!
It's pretty finicky.
Basically, Wx/W8 dual booting can be set up to work properly IF you already have a dual or multi boot system installed, using the VI/7 OS boot system.
Otherwise, well, pot luck...
Here's how I did it :
0) Obtain a good W8 DVD
1) Install a second copy of W7 (Vista or 2008 would work just as well), on a new partition and/or hard drive
(the ONLY purpose here is to create a dual boot system using BCD Store)
2) Use VBP/DBP to edit the boot menus appropriately (this can be done later, but it's important to do so in VI/2k8/7 -- NOT 8) -- why now ? well, this is the only stage where it's completely risk-free.
3) reboot, with the W8 DVD in the drive, and install W8 into the desired partition
(this will create the current W8 multiboot environment, where booting into a different Windows version is controlled by W8)
4) In the W8 boot screen, select "Change defaults or use other options", and select VI/2k8/7 as your default OS -- this will restore the legacy VI/2k8/7 boot menu
4b) you will need to test it if "Older Operating System" AKA XP will work as a valid OS choice in this scenario, sorry
5) Boot into VI/2k8/7, and use VBP/DBP to choose which OS as default, change order of display OS, and etc as normal
here, I've already seen VBP messing up boot simply because I was being overzealous, and basically misusing it)
Hope this helps !!!