Other look for XP
It's a little old already. But I'v found a way to giv XP a new look, using MS software only.
Download the file using the this Google link.
Right click (you can't run it as it will say only available for Xp tablet etc) the downloaded EXE file and extract its content to a local temp folder C:\temp\theme.
Create the following folders under the C:\WINDOWS\Resources\Themes folder: (I just copied Luna and renamed and deleted extra files)
Copy the royale.theme file that you extracted into the main C:\WINDOWS\Resources\Themes folder.
Copy the royale.msstyles file into the \royale subfolder.
Copy the shellstyle.dll file into each of the \shell subfolders (royale\shell\homestead, royale\shell\metallic, royale\shell\normalcolor, royale\shell\royale).
Copy the energybliss.jpg file into the \royale\wallpaper subfolder.
When you select the Display Properties Appearance tab you will see two Windows XP style options listed.
One of the style options includes a Royale color scheme (XP automatically selected this, butr just check); select this scheme then on the theme tab, select the Energy Blue theme.
(Copied from http://geekswithblogs.net/jking/archive/2004/11/04/14345.aspx)