If these are msstyle themes you need to replace the uxtheme.dll file.
You can get it here:
XP Service Pack 1
http://www.softpedia.com/get/Desktop-Enhan...-included.shtml
XP Service Pack 2
http://www.softpedia.com/get/Desktop-Enhan...SP2-Final.shtml
XP Service Pack 3
http://www.softpedia.com/get/System/OS-Enh...ws-XP-SP3.shtml
Now you are ready to replace your uxtheme.dll file
The replacer can be downloaded here:
http://www3.telus.net/_/replacer/
1. Now double click on the replacer file (replacer.cmd)
2. Then it will ask you to drag and drop the original system file you want to replace. So go to the System32 folder and somewhere near the bottom you are going to see the uxtheme.dll file. Drag and drop it into the window.
Note: your computer may have more than 1 uxtheme.dll file but usually the file that your computer is using is the one in the system32 folder. (usually the location for your Uxtheme.dll file is C:WINDOWSsystem32uxtheme.dll)
3. Press Enter
4. Then it will ask you to drag the file you want to replace. Open the folder with the downloaded file and drag and drop the file into replacer.
5. Now it will ask you to confirm that you want to replace the files or not. So double check and then press enter.
Replacer will now swap your original file with the new one. Now restart your computer.
Congratulations you can now use custom msstyle themes on your computer.