Question Can I use Windows xp machine as a file server to my Google MXQ running Kodi 18?

Theoretically, you can, by using the SMB protocol, but by now, Windows XP is pretty old, and insecure of file server needs. Have you considered installing a linux distro to your windows xp home server machine?

Also, considering that it runs Windows XP, I bet the computer is pretty old as well, so don't expect the fastest file server with that machine.