the more I think of it, having two separate /homes (Old/home and New/home, though I assume these are just labels and not mount points/paths. The paths would be /home/new/[user name] and /home/old/[same user name?]?) makes more sense to me considering that I'll have the reference of the Old/home available to draw on in building the New/home that suits my needs with the 12.04 version.
But I'm not quite clear on the partitioning method (though you've provided good explanatory screenshots, and I'm just flat out dense about this . . . as you can see in my stated confusion about the home paths above), so let me state here what my understanding is, and please correct me if I'm wrong.
1. On the creating and sizing, you suggest creating a partition (from the unallocated portion) destined for the 12.04 system (New/? Just a "label", right? So would I give it a mount point, and then how would this be seen as different from the 9.10 /?)
2. And then another formatted and sized partition from the unallocated partition destined for the 12.04 home (New/home? Just a label, right? Same question, how would the mount point of the 12.04 /home be seen by the boot as different from the 9.10 /home? Wouldn't the system get confused and cranky? Or does the fact that they are on different sda designations take care of that?)