the last version of windows that ran on MIPS was windows NT4.
essentially, yes, you can probably still find that at yard sales and thrift shops, but no, you will not find drivers for it, most modern software won't work, and whilst you might find a copy of visual studio 6 to write your own software, you'll be treading a lonely path.
If you want a small board, and you plan to develop some apps on it then you have a bunch of options...
1, run linux on a small form computer.
by small form computer I mean, Raspberry pi, or Raspberry Pi 2, or beagle board, or the Olimex Lime boards, Bananna Pi etc. develop an app in a non-platform dependant language, - like Java.
this is my preferred approach, except I'm not "developing" apps, I'm just using existing apps, the power saving of using a small (5w) board over a 200W desktop is significant enough to pay for the thing inside a year.
2, run windows on a small for ARM computer, certainly Raspberry pi 2 is on the "official support list" for MS's internet of things IOT program.
I believe that the cut down version of windows (simillar to windows RT?) is free on these devices...
BUT, don't think that you'll be running any applications compiled for x86 x64 architectures, just like the original surface RT tablets than had ARM processors the list of apps that can run is small (but if you're writing your own software then again go nuts. whilst I think less people are doing this, it's not going to be anywhere near as lonely as trying to use windows NT4!
3 Run windows on an x86 small form factor board... for example the intel galileo. upsides, proper 32bit environment.
downside, not fast, not featureful, not cheap.
upside, real windows real 32 bit, real applications with less hassle.
4, grab something from car PC manufacturers, lilliput have been making small form PCs that run off DC for years, they arn't dirt cheap, but they aren't expensive either. you get full OS full apps. etc.
5, go for a "set top" type box.
i can't remember the model name but Futitsu did (a friend had one) used to sell a box that was fanless ultra quiet, small form and Vesa mountable, (which in practical terms meant you could hide it away by mounting it on the back of your TV.
modern day if you search for baytrail on amazon or aliexpress you'll find a bunch of machines with modern 64bit architectures, that can run on battery power, have decent amounts of RAM in them. and start at around £100 GBP (sometimes less) for a manufactured properly cased product that runs windows out of the box and has a decent case, USB ports, HDMI connections etc.
e.g. looks good, works good runs full windows with all the apps.
The baytrail (atom) chip is what's powering a lot of Surface clones.