OleDbConnection dbConnection = new OleDbConnection (@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\BAR.XLS;Extended Properties=""Excel 8.0;HDR=Yes;""");
dbConnection.Open ();
try
{
    // Get the name of the first worksheet:
    DataTable dbSchema = dbConnection.GetOleDbSchemaTable (OleDbSchemaGuid.Tables, null);
    if (dbSchema == null || dbSchema.Rows.Count < 1)
    {
        throw new Exception ("Error: Could not determine the name of the first worksheet.");
    }
    string firstSheetName = dbSchema.Rows [0] ["TABLE_NAME"].ToString ();

    // Now we have the table name; proceed as before:
    OleDbCommand dbCommand = new OleDbCommand ("SELECT * FROM [" + firstSheetName + "]", dbConnection);
    OleDbDataReader dbReader = dbCommand.ExecuteReader ();

    // And so on...
}
finally
{
    dbConnection.Close ();
}