Risolta la conversione, la posto se può essere utile a qualcuno:
Imports Microsoft.Office.Interop
Public Class Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim fileXls As String = "d:\origine.xls"
Dim fileCsv As String = "d:\ddestinazione.csv"
Dim oExcel As Object
oExcel = CreateObject("Excel.Application")
oExcel.Workbooks.Open(fileXls)
Dim oBook As Excel.Workbook
Dim oSheet As Excel.Worksheet
oBook = oExcel.ActiveWorkbook
oSheet = oExcel.Worksheets(1)
'salva
oExcel.DisplayAlerts = False
oBook.SaveAs(fileCsv, 3) ' 3== csv
oBook.Close()
oBook = Nothing
MsgBox("fatto")
End Sub
End Class
Grazie ancora a tutti