I think I got the hang of it. I have not created a separate /boot partition yet. I installed Linux Ubuntu 8.04 “Hardy Heron” on my second target partition. The first of the five available partitions is currently being occupied by Linux Mint 5 “Elyssa”. I’ve been doing a lot of reading about Grub and practicing on it on Mint 5’s menu.lst. It now has all the OS of my 2 machines – Sempron Desktop and Sony Vaio laptop. So as long as I’m using Grub, I think I’ll be fine. I’m now rethinking that separate /boot partition. It looks like my current setup is fine. I can wipe out my Ubuntu 8.04 practice installation and put Mandriva One or OpenSUSE 11.0 KDE4 over it.
On another note, I’ve been able to successfully boot my Western Digital Scorpio drive containing all of this between the 2 computers mentioned above. All I needed was to edit the menu.lst and use /dev/sdb5 when on the laptop and sdc5 when on the desktop. Then boot into recovery, fix X and boot the normal way. It’ll ask for the proprietary video drivers again since the former has ATI and the latter Nvidia. One more reboot and all is set.
BIOS reads the USB drive as first while the OS thinks it’s last. The BIOS part is true for both machines that’s why I didn’t have to edit that part. All seems well at multi-booting, Grub menu editing and switching machines. Everything I’ve tried works including wireless. Now I just have to finish the downloads.