The .NET FolderBrowserDialog class does not have an InitialDirectory property like the OpenFileDialog class.  But fortunately, it’s quite easy to set an initial folder in the FolderBrowserDialog:

FolderBrowserDialog dialog = new FolderBrowserDialog();
dialog.RootFolder = Environment.SpecialFolder.Desktop;
dialog.SelectedPath = @"C:Program Files";
if (dialog.ShowDialog() == DialogResult.OK)
{
    Console.WriteLine( dialog.SelectedPath );
}

Note that you can choose other RootFolder’s like MyComputer and MyDocuments.  The SelectedPath must be a child of the RootFolder for this to work.

Given the sample code above, the dialog may look like this: