I don't think you really can find any drivers for modern components to natively use Windows XP. Your most likely going to have to use a virtual machine to use Windows XP.
That area is out of my specialty so I can't comment on it much. What connections do you need to run the CNC? And since Windows XP is very out of date it's usually recommended to keep this machine off the internet and just transfer files via USB key from what I've heard most people in this situation do.
Hardware wise, I doubt you need much. A low end build will probably suffice, though just in case what kind of budget do we have to work with?
I'd remecomend a system that is something along the lines of:
AMD Ryzen 2200G
A cheap case with decent airflow
A decent good power supply like a Corsair CX450 or EVGA 500B
How ever much storage you need, preferably with SSDs.
That should probably cost you no more that $400.
It would have decent CPU power and not horrible graphics power.
It would also be on an upradeable platform that would alow for upgrades if they are needed.
Hope this helps, Let me know when you have a final parts list or if you need more help.