How to save the text file in the Documents folder

In a CLR project, windows form,I use SaveFileDialog control and richTextBox->LoadFile  to save a text file:

private: System::Void viewlog_Load(System::Object^ sender, System::EventArgs^  e) {
		richTextBox1->LoadFile("log.txt",RichTextBoxStreamType::PlainText);
	}
private: System::Void button1_Click(System::Object^sender, System::EventArgs^  e) {
		saveFileDialog1->ShowDialog();
		if(saveFileDialog1->FileName != "")
	    	{ 
                 richTextBox1->SaveFile(saveFileDialog1->FileName,
                 RichTextBoxStreamType::PlainText);
                }
        }

The Savefile control opens of default in installation folder. (Of course the user can change the folder manually).
How can I make because the control is opened by default in the Documents folder?
The sample code of VS Help does not work:

public:
   void SaveFile()
   {
      // You should replace the bold file name in the 
      // sample below with a file name of your own choosing.
      richTextBox1->SaveFile(String::Concat
         (System::Environment::GetFolderPath
         (System::Environment::SpecialFolder::Personal),"\\Testdoc.rtf"), RichTextBoxStreamType::RichNoOleObjs);
   }

I work with VCExpress2010 and xp.

beginner of planning