There's a desktop for Windows written with Delphi named #E (AKA SharpE). I didn't test it and I don't know if it's open source or similar but may be you should take it a look.
I will soon create a Wiki page where my project will be described in details and who wants can participate.I just wanted to add that when installing on Windows a program like Co-Linux or andLinux, we also have a kinda replacement DE for Windows, only the desktop is the same. So this is possible.
A cross compatible Desktop Environment, not that difficult with Lazarus/FPC.The main idea behind this project is to create a Desktop Environment which will work on Windows, GNU/Linux and MacOS X systems at least, maybe more in the future.
My suggestion is to use the GTK2 toolkit, because this is much easy to use and works on all 3 the systems, while other toolkits don't always.