Hi, you should be able to install grub on both drives, chained/linked to each other.
With Mandriva, I know I can use grub to boot an external hdd.
Similarly, I have winxp (sdb1) Mandriva (sda1), and for quite some time I had a reat-time kernel on sdc1.
The mandriva tools for setting up grub, the boot loader, automatically searches and lists all the OS's installed on the system.
Just use "MCC/boot/setup boot system/next/Add and follow the prompts".
With the click of a button I can add or remove the reference to any of these OS's.
No rebooting required.
Notice that the namenclature is different, first drive = hd0,n, where n = partition number.
/boot/grub/menu.lst.example (you need root access to edit and save this file)
viewport 3 2 77 22
kernel (hd0,4)/vmlinuz-2.6.11-8mdk root=/dev/hda6 resume=/dev/hda1
I hope this gives you something to look for, Regards Glenn