I'm making a little more progress on this. I just built (on Ubuntu 12.04) a minimal i386 VM with QEMU with ReactOS 0.3.17 (notes below). Next I hope to add fpcup (or something similar) to compile trunk to get an embedded ARM compiler which I hope to use with Teensy
https://www.sparkfun.com/products/12646.
Download
http://reactos.org/ ReactOS-0.3.17-REL-iso.zip (88MB) and unzip to get ReactOS-BootCD.iso (103MB)
qemu-img create -f qcow2 reactos0317.img 2G
qemu-system-i386 -m 512 -hda reactos0317.img -cdrom ReactOS-BootCD.iso -boot d
For the install I just pressed <Enter> for everything. When it reboots (twice) don't hit any key so it won't boot from the CD.
Shut down ReactOS. The QEMU image file is 280MB.
Restart with networking:
qemu-system-i386 -m 512 -hda reactos0317.img -boot c -net nic -net user
In the VM (I hope to edit this more ASAP):
Double-click on the Command Prompt and run ipconfig.
I installed Firefox 3.6 (28 and 37 had problems) with the ReactOS Application Manager and then downloaded
https://github.com/LongDirtyAnimAlf/Reiniero-fpcup fpcup.exe and ran it. There are several problems that will hopefully be solved soon.
No, you don't want to use ReactOS for your desktop operating system, but it might be good enough to use for some specific things (like putting in a small VM). I've had a bit of fun with ReactOS for some time:
http://turbocontrol.com/reactos.htm