There are a number of system folders available in Windows Vista/Seven. This
article[
^] describes what each of the system folders are and where in Windows Vista/Seven the folders map to by default.
Global shared data usually gets mapped to C:\ProgramData, for example. User specific data is usually mapped to C:\Users\[username]\AppData\Local or C:\Users\[username]\AppData\Roaming. If you're maintaining compatibility with Windows XP, it's best to use the %AppData% environment variable rather than the %LocalAppData%, as the %LocalAppData% EV doesn't exist in Windows XP.
To access these locations in .NET, check out Environment.SpecialFolder in the MSDN documentation.
Hope this helps.
Flynn