Saving a document in shared folder

Hi I am under a task (in my wpf project) to save a document in shared folder,so any user of that system can view that document .

I want to know how i can get the shared folder path i.e(c:\users\public\documents) in windows 7 as well as in xp or in vista Os to save that document,

Pls provide me a solution regarding this

Thanks in Advance

Efforts may fail but don't fail to take effort -------------- sidd