Ok let's reclarify somethings here:

Windows was NOT ported to the MIPS processor. The image is still very much x86. The emulator was running it so it could switch the x86 code to MIPS.

Another thing: To get something like say Windows Mobile or Palm OS onto a Nokia 770 you would need a licensee agreement from Microsoft or Access which will run you a couple million dollars.

Or you could reverse engineer the entire OS which is illegal and could land you in jail.

In short what you want to do is nearly impossible and/or illegal. I for one think a simple emulator that would run on top of Maemo such as a Palm one (since Palm OS was built for really limited hardware say a 22mhz monochrome screen).