However there are some good themes for those third party programs out there. The program I use to theme Win2k is called WindowBlinds. It's made by a company called Stardock
and it's cheap too (like 19 dollars).
You can find themes for it at places like Deviant Art
or even at the Stardock website.
also makes other programs that allow you to change the default system icons (like the icons used for the different folder types), change the way windows appear on screen (transparency anyone?....even have windows fade in when they appear, instead of just 'popping' up). and even change the way the desktop works.
Check out their site, they have some cool sh*t there.
Here's a desktop that was made using their apps. This is the ENTIRE desktop (taskbar, system tray and all that have been changed/modified).