There have been some complaints that Microsoft was not going to fully support netnooks with Windows 7. However this does not seem to be the case as we find that Intel's next gen Pinetrail Atom will be supported by Windows 7.
Support will come in the form of the two simplest flavors of Windows 7 (home basic and starter). However, I can say from personal experience that the current Atom (N270) with Intel's chipset will run Windows 7 Ultimate (RC1 Build 7100) as I have it running on an MSI Wind U100. I did have to bump up the RAM to 2GB but I would have done that anyway.
So netbook users do not fear, Windows 7 will run on your favorite new toy. You just won't be able to buy a netbook with Windows 7 Ultimate preinstalled.
Read more here.
Intel is quite sure that its upcoming Pine trail-M platform will support at least two versions of Windows 7. Intel has informed its valuable partners that Pinetrail-M, mobile platform that includes N450 CPU and NM10 chipset will support Windows 7 Starter and Home basic.
Since a lot of people already tested Diamondville, Atom based notebook and windows 7 RC1, we already know that all Windows 7 versions should be able to run on existing and future Atom platforms, but Microsoft will definitely want to draw a line, and limit some Windows 7 to more expensive notebooks.