Win98se And Xp Themes: Differences?

Hi! I have a Win98SE tower and a WinXP laptop at my mother's house and like themes for them. In fact, I've been downloading a lot of them recently. I go to archivde.org for the themes and sometimes find some for WinXP. I probably shouldn't download the XP themes, as my WinXP system is not in good shape. I may want to get that system a new power supply soon, because one of its problems is a dead battery. I'm wondering if I should hook it back up and, if I do, the difference between Win98 themes and WinXP themes, as, currently, I download everything to one folder and need to determine for which system a theme is made.