//MyDocument内のパス取得
string dirMyDoc = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + “\\xvax";

//パス上にディレクトリ存在しない場合
if ( Directory.Exists(dirMyDoc) == false ) {
	//ディレクトリ作成
	Directory.CreateDirectory( Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + “\\xvax" );
}

//NT LOGIN Name
using System.Runtime.InteropServices;

[DllImport("Advapi32.dll", EntryPoint = "GetUserName", ExactSpelling = false, SetLastError = true)]
static extern bool GetUserName([MarshalAs(UnmanagedType.LPArray)] byte[] lpBuffer, [MarshalAs(UnmanagedType.LPArray)] Int32[] nSize);

byte[] str = new byte[256];
Int32[] len = new Int32[1];
len[0] = 256;
GetUserName(str, len);
//ex
lblLogName.Text = System.Text.Encoding.ASCII.GetString(str);