What determines where GRUB is installed?

[mtyoung]

I have 3 hard drives on my system.

Drive 0    ATA           20GB with an old Ubuntu 6.04 system, and, I 
believe, my original Grub.
Drive 1    SATA 2    200GB with a freshly installed LinuxMint 2.1
Drive 2    SATA 1    160GB with an old Windows XP system, and I believe, 
my new Grub.

When I originally installed Ubuntu, I'm pretty sure Grub was installed 
on the same drive, because changing the boot sequence in BIOS setup 
determines whether or not I see Grub during a boot.

When I installed LinuxMint I disconnected the Ubuntu 20GB drive, to 
prevent any chance of it being effected.

If the SATA200GB with LinuxMint is first in the boot sequence, I get an 
error which says that no operating system can be found.

When I set the SATA160GB with XP as first in the boot sequence I get the 
new Grub menu, and can choose to boot XP or LinuxMint.

When I set the ATA20GB with Ubuntu as first in the boot sequence I get 
the original Grub menu, and can choose to boot Ubuntu or XP. If I choose 
XP there is a quick flash of text which I don't remember every seeing 
before. Almost as if the old Grub sees the new Grub and then skips past 
it. But, to clarify, I can't read the text fast enough to really tell 
anything, so its a guess.

I did change the physical drive connections when I installed the 
SATA200GB drive (because I had problems with SATA 2 working with by 
chipset) and this was between the times I installed Ubuntu 6.04 and 
LinuxMint 2.1.

So, what determines the drive that Grub is installed on? Is it the first 
drive in the boot sequence, or first in the BIOS connection order 
(forgot what that's called at the moment), or is it strictly a function 
of the installer, and LinuxMint is just different for no good reason?

I have an image backup for the XP drive, so I can restore it, but how do 
I force Grub to install where I want it?