There is a new theme available for windows XP and Server 2003, the theme is extracted from the Windows Embedded Standard CTP Refresh. This is an official theme so there is no need to touch system files.
To install the theme download the archive from here, unzip it and run the .EXE file. After installing select the new theme from desktop properties. The theme looks good, bue and shiny if you want to some different look than the default theme give it a spin. This theme works with both windows xp and windows server 2003. Thanks to Askvg for discovering this.