You might have seen that it is not possible to install themes directly in Windows XP. You need some software to install themes. So here are two methods of installing themes in Windows XP.
1. First method is by using UXtheme patcher. It is a simple method. First of all download and install UXtheme patcher. You can download UXtheme patcher from here. Now download any theme and unzip it to C:\WINDOWS\Resources\Themes. Now right click on Desktop > Properties > Appearance and Choose your theme and apply. That’s all.
2. Second method is by using TuneUp Utilities. I use this method as it has some other benefits also. Download TuneUp Utilities and use it to install themes. You can download TuneUp Utilities from here