Here is a new theme for Windows XP and 2003 users. Its called "Embedded" theme. Its an official Microsoft theme so you'll not need to patch anything. You can apply it without any problem.
This theme has been taken from "Windows Embedded Standard CTP Refresh" and works perfectly in Windows XP and 2003.
Download following ZIP file, extract it and run the .EXE file. After that you can apply the theme from Desktop Properties. A sweet wallpaper is also included in the pack.
PS: You'll find the download link in the right-side section of the above mentioned page.
All credit goes to Microsoft for this excellent theme. We are just sharing it. :)