let me provide you a short answer. What you are trying to do is either not going to work, or else be a lot more trouble than it's worth.
Here on this forum there is a policy against cloning Windows XP from one computer to another unless both computers are identical and both have the Windows XP product key. It has been suggested that owning Windows 10 would entitled you to use Windows XP also. But this is not really a policy of Microsoft. In fact, Microsoft does not encourage the continued use of Windows XP for anything.
Now that, after having said that, here are some points you want to consider.
Windows XP must be the first operating system installed on the hard disk. The hard disk must be formatted completely to the type of structure used by Windows XP. Specifically, Windows XP wants a hard drive formatted to what is called the MBR format.
May I suggest that if you wish to explore more about Windows XP, just use it on your old computer. You may be able to make space in your personal office to have both computers on your desktop. You can get a switch to switch back and forth between computers and your monitor. That is, in my opinion, the easiest and most effective way to enjoy to operating systems that you are to have installed.
Doing a dual install of Windows tenant and Windows XP will probably take more time than what you were spending. And the end result is not as good as having two separate computers. And this is not just my opinion, many others will tell you the same thing.