Microsoft just wants money, but if just using an XP computer it probably will have no problem unless your anti-virus don't work, but then again, software won't be made for it probably any more.
A person could use a Windows 98 computer if you have the drivers for all of your hardware, but if buying new hardware, then they may not have drivers made for Windows XP anymore, so the computer will work with old hardware and drivers that still were made for XP.