If you plan to re-use XP again, then most newer mtrbds. don't really support it. Find a mtrbd. you like and plan to purchase then check its support website and see if XP drivers are part of the support. I assume your current install XP disc is the early DIY type and generally is like the retail version, so it isn't locked to your old PC. As long as you install on (1) PC it's OK to re-use. Once you buy your new mtrbd. you get whatever new items/devices you need to have the newer version or latest because I'm sure you have dated devices and you wouldn't benefit that much by re-using them. So, I suggest you look for a "white box" or "bare bones" PC so you can re-use your monitor and probable USB kybd./mouse or upgrade to that. Just look at what's offered out there is leaps and bounds better than your old P4 system.
As for XP service packs, you can still get them from MS or trusted file sources. Just have the SP3 alone will be enough as it carries all previous SP with it.
I have my XP running on my rather old hardware, P4 processor,2 G memory and a motherboard, "matsonic MS9327E(USB).I really can not remember the date I bought this computer.
I have been using my XP off and on for years it gave good service. Now it appears to be rather slow for my liking. I would like to change the motherboard,processor and other peripherals to make it faster as fast as the XP can go.
I shall be grateful for some advice on the motherboard.
I use this computer for email,occasional letter writing and very occasionally for photo printing.
I have the original key for the product and the disc, I am not sure what would I do about the additions ,Paks 1,2,and 3 !
All the same if I can find a suitable motherboard without spending a fortune I will sort out the other things.