In order to use unsigned/un-official visual styles (visual themes) on Windows XP/SP1/SP2 Beta/RTM and 2003, you must first patch your UXTheme.dll file. The UXTheme Multi Patcher (download below) will patch the UXTheme.dll file automatically. And will allow you to use all Windows XP SP1/ Windows XP SP2 Visual Styles and Themes available. (Including the themes here on GuiCentral.com)

Download Windows XP UXTheme Multi Patcher

 

Alternative method to patch UXTheme.dll:

If for some strange reason the Windows XP UXTheme Multi Patcher doesnt work for you, try this:

1- Get the appropriate uxtheme file from here: http://www.withinwindows.com/uxtheme-patches/

2- Then download Replacer: Download Replacer for XP Themes

3- Extract the contents of replacer to a new folder, run replacer.cmd and drag in the original uxtheme.dll, then drag in the modified uxtheme.dll that you downloaded, and let it replace the file.
4- Reboot / Restart your pc when asked.