Microsoft is unfortunately moving toward web forums and away from newgroups for support. At this time, Microsoft has no newgroup for Windows 7 and may never have one.
There are a series of Vista forums underneath microsoft.public.windows, but nothing I can find for Windows 7.
There is alt.windows7.general, but it has little traffic.
Microsoft has a series of forums (not newsgroups) at: Windows 7 IT Pro Category