This is how to open a system folder in C#:
string myDocspath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
string windir = Environment.GetEnvironmentVariable("WINDIR");
System.Diagnostics.Process process = new System.Diagnostics.Process();
process.StartInfo.FileName = windir + @"\explorer.exe";
process.StartInfo.Arguments = myDocspath;
process.Start();
Source: http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/ce864f19-25c1-4601-a1ff-6019c703ccdb