using System;
using System.IO;
using System.Text;

namespace RegTest
{
    class EntryPoint
    {
	static void Main(string[] arg)
	{
		FileInfo fi = new FileInfo("test.out");
		TextWriter w = fi.AppendText();
		w.Write("Здравствуй мир!");
		w.Close();
	}
    }
}

Dim out as New IO.StreamWriter ("test.out",True , system.Text.Encoding.Unicode )

System.IO.StreamWriter w = new System.IO.StreamWriter("test.log",true,Encoding.GetEncoding(866));
w.Write("Здравствуй мир!");
w.Close();