If I am not an Administrator and start a program which writes to C:\\ some textfile - will I need admin rights...in Windows 7 or Vista? I see in XP there are no problems to writ
That depends on whether C:\ is a filesystem that supports permissions, and if so on the permissions set on the root directory, which can be modified by users with the correct privileges. Use GetTempPath() for temporary files, or SHGetFolderPath passing e.g. CSIDL_APPDATA