Convert XLS to tab delimited.

Use ADO and the Jet OLEDB provider, which can read the contents of excel files without actually opening Excel.

Example:

'*******************************

Public Sub ConvertXLSToTab(ByVal xlsFileName As String, ByVal tabTextOutputFile As String) 
        Dim connectionString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source='" & xlsFileName & "';Extended Properties='Excel 12.0;HDR=YES';"
        Dim strSQL As String = "SELECT * FROM [Sheet1$]"
        Dim excelConnection As OleDb.OleDbConnection = New OleDb.OleDbConnection(connectionString)
        excelConnection.Open()
        Dim dbCommand As OleDbCommand = New OleDbCommand(strSQL, excelConnection)
        Dim dataAdapter As OleDbDataAdapter = New OleDbDataAdapter(dbCommand)
        Dim ds As New DataSet
        dataAdapter.Fill(ds, "dTable")
        'DataGridView1.DataSource = ds.Tables("dTable").DefaultView
        Dim strLine As String
        Dim objStreamWriter As StreamWriter
        objStreamWriter = File.CreateText(tabTextOutputFile)
        For Each row As DataRow In ds.Tables("dTable").Rows
            Dim column As DataColumn
            strLine = ""
            For Each column In ds.Tables("dTable").Columns
                If (strLine <> "") Then strLine = strLine & vbTab
                strLine = strLine & row(column).ToString()
            Next column
            objStreamWriter.WriteLine(strLine)
        Next row
        excelConnection.Close()
        objStreamWriter.Close()
    End Sub