private String[] GetExcelSheetNames(string excelFile)
{
  OleDbConnection objConn = null;
  System.Data.DataTable dt = null;

  try
  {
    String connString = "Provider=Microsoft.Jet.OLEDB.4.0;" + 
        "Data Source=" + excelFile + ";Extended Properties=Excel 8.0;";
   
    objConn = new OleDbConnection(connString);
    objConn.Open();
    dt = objConn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
 
    if(dt == null)
    {
      return null;
    }

    String[] excelSheets = new String[dt.Rows.Count];
    int i = 0;

    foreach(DataRow row in dt.Rows)
    {
      excelSheets[i] = row["TABLE_NAME"].ToString();
      i++;
    }

    for(int j=0; j < excelSheets.Length; j++)
    {
      MessageBox.Show(excelSheets[j]);
    }

    return excelSheets;
  }
  catch(Exception ex)
  {
    return null;
  }
  finally
  {
    if(objConn != null)
    {
      objConn.Close();
      objConn.Dispose();
    }
    if(dt != null)
    {
      dt.Dispose();
    }
  }
}