Scrap

foreach($file in (Get-ChildItem "C:\temp")) {

 $newname = $file.FullName -replace '\.xls$', '.csv'
 $ExcelWB = new-object -comobject excel.application
 $Workbook = $ExcelWB.Workbooks.Open($file.FullName) 
 $Workbook.SaveAs($newname,6)
 $Workbook.Close($false)
 $ExcelWB.quit()

}