I am looking a mail reader that runs on windows7 and gives me a Group buffer very similar to gnus. Where I can order the groups easily and hide all groups below a certain priority.
Gnus on windows is broken so that is out of the question.
Using Mozilla Thunderbird you would be able to get towards your goal by creating a numbers of "saved search" folders (From File->New->Saved Search)
The virtual "saved search" folders can run a set of defined search rules over any set of real mail folders (even across different e-mail accounts) that you wish.
Unfortunately it does not solve being able to pick the order that these are displayed in.