MinWin is not so much a product as it is a continual effort starting with Vista to untangle dependencies and move unnecessary cruft out. It's still the NT kernel, only progressively cleaner with each additional release of Windows.
Before Vista came out I managed to cut down an XP image to ~200MB in ISO form and less than 300MB on a "fresh" install on real hardware ("fresh" because it was Service Pack 3+ slipstreamed into the install ISO).
That was basically the bare minimum needed to run the OS on my laptop with wifi and sound.
Put something similar on my EeePC 701 when I got it, having a 6/7 second boot time on Windows was quite nice;
