I was poking around with this the past two days. And I successfully "ported" and compiled the Windows CE Desktop Environment Shell source code to Dreamcast
The code is Microsoft's original code and is unmodified with the exception of a few additional header files, I just had to add additional libraries and track down missing header files for it to build for Dreamcast
Only problem is, it seems it will take a little more work to get this to run on the Dreamcast. I don't really have the skill to take this further
You can download the source code here
https://github.com/FaucetDC/WincastCE
It's ready to compile "out of the box" as long as you follow the instructions
It'd be cool if someone more skilled than me gave this a go
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https://msdn.microsoft.com/en-us/library/aa452726.aspx
https://msdn.microsoft.com/en-us/library/aa453936.aspx