Microsoft offer tons of Windows 7 themes and you can download and use those Windows themes for free. However, Microsoft doesn’t allow third-party themes to make major changes to your OS.
You can still manage to do so, by tweaking and patching some system files i.e uxtheme.dll, themeui.dll, themeservice.dll. Universal Theme Patcher is a free utility which patches these 3 files so you can download custom Windows 7 themes and use them on your computer.
In spite of all the problems that have come with Windows XP SP3, people are still using it. If you are also one of them, then you must have noticed that your 3rd party Windows XP themes have not be working after installing service pack 3. That’s because the uxtheme.dll has been changed.
To fix this, you will need the UXtheme Patcher in order to run any 3rd party themes on Windows XP. Download it from here [direct link] and run the EXE file. Press the Patch button, and wait for a few seconds for it to patch. Now restart your computer for the changes to take effect.