PRUEBA CON ESTO
Dim s As New StringBuilder
Dim a, b As Integer
TextBox1.Text = ""
s.Append("<Table>")
s.Append("<tr>")
For b = 0 To Tabla.Columns.Count - 1
s.Append("<td>" & Tabla.Columns(b).ColumnName & "</td>")
Next
s.Append("</tr>")
For a = 0 To Tabla.Rows.Count - 1
s.Append(" <tr> ")
For b = 0 To Tabla.Columns.Count - 1
s.Append("<td>" & Tabla.Rows(a).Item(b).ToString & "</td>")
Next
s.Append(" </tr> ")
Next
s.Append("</Table>")
Dim FilePath As String = "C:\nombreArchivo.xls"
TextBox1.Text = s.ToString()
Dim strStreamW As Stream
Dim strStreamWriter As StreamWriter
strStreamW = File.OpenWrite(FilePath)
strStreamWriter = New StreamWriter(strStreamW, _
System.Text.Encoding.UTF8)
strStreamWriter.WriteLine(s.ToString())
strStreamWriter.Close()