Minwin

"It amounts to around 150 binaries, and requires 25MB disk space ..."

A little way to go yet, Microsoft. I remember a QNX demo FLOPPY a few years back that had a windowing system, TCP/IP, a web browser, etc. On a fricking floppy.

I always like playing around with minimal installations. I've wasted countless hours doing trial and error Solaris minimal installs. Just for fun. I wouldn't know where to start with Windows.