The current Windows version of iTunes (v12.2.1.16) requires Windows 7 or later, to run properly.
In order to get your iPod Classic to work on iTunes on Windows XP, you will need to do a google search for a search term something like: "older iTunes downloads for XP". I won't provide search links for you, as I don't want to accidentally link you to malware or other nasty stuff - you'll need to find it yourself. However, there are plenty of shareware sites out there that still have older versions of iTunes Installers that will work on Windows XP.
Best of luck to you!