Start with Old Gaming on Windows XP

3rd post in the past 3 days, sorry about that. Anyways, I would like to get started with old gaming on XP and decorate my computer in general. It would be cool to have certain themes for my computer, I’m looking for kind of a dark color theme to match a dark-ish wallpaper. On the old gaming aspect, are there any ways I can be directed to find what I need? Any help or tips would be appreciated.