as you have 2 drives you have about 3 main options.
Assuming ms=windows has an error ...wt? lol
Option 1) Change bios boot order to drive 2....which I will calll the linux hd.....and remove from bios option the ms drive which currently has the alleged grub2 in it and chainloades to ms
then boot the live cd....and run command on from ubuntuo
...the response should show only one drive which from bios order change is now /dev/sda...hit space bar to select and allow grub2 into that mbr.
Now remember...grub2 is still in mbr of drive1 but it now on drive2 as well...ok?
to boot linux from now on....change bios boot order to linux hd
/etc/fstab should not need changing if UUIDs are in it.
/boot/grub/grub.cfg should also have UUIDs so no changed needed.
Now still in option (1)...reset bios to ms drive and disable linux drive.
use windows dvd to restore = recovery mode....fixmbr.
this overwrites the mbr of drive1....deliberately and linux mbr is gone.
To boot ms...change bios boot order to drive1
to boot linux change bios boot order to drive2
Keep existing boot order
allow ms to fixmbr of its first drive....loosing linux.
use a linux live cd to install linux grub2 into the "root" of the boot partition....and edit ms to chainload linux.
my legacy style signature has info on this.
Then you no longer have to be scared of overwrites.
Option (3) is messy to explain but bear with me
a) to boot ms....you first your windows recovery to fixmbr for mbr drive 1..same as option (2)
b) put grub2 into mbr of drive2 ...a bit like option (1) but no bios boot order change
c) when ms starts....hopefully there is F12 key or F8? that allows you to change hard drive order?
so to boot ms....no pressing F keys
to boot linux press whatever F (number) needed
2) The explanation of alleged ms bootloader overwrite may be due to your computer manufacturer....using a recovery partiton.
When changes are made no consistent with how it first was active....the sytem will revert (restore) and older mbr