This has gotten kind of complicated, but one thing caught my eye, about boot partitions and all that. Usually the primary partition "C" is where the OS is installed, I haven't experimented with multiple os in the same drive so can't comment on that, but my impression is that you can only have one bootable partition on a drive, so if you wanted to put in a second one, you'd have to make the first one not be bootable anymore. As I recall, I've read of making a small bootable partition when there is more than one os, which has a menu of options and acts as the boot manager so you can pick which one you want to run, with each os having its own partition. If you wanted to try that, you would have to use a partition manager to move the existing XP installation into its own partition away from C, and obviously shrink the old boot partition to just what you need for your boot manager, create a third partition or however you want to do it, for the new XP installation and go from there. You should look up boot managers for more information. Apparently XP actually has its own boot manager, but is only included in the Pro version. I think I actually used it myself, but I've forgotten the details. Try here to start: https://www.oreilly.com/library/view/windows-xp-in/0596002491/re54.html