$Excel = New-Object -Com Excel.Application

foreach ($File in (gci *xls)) {
$Workbook = $Excel.Workbooks.Open($File.FullName)
$Workbook.SaveAs(($File.FullName + "x"), 51)
$Workbook.Close($false)}

$Excel.Quit()

$Excel = New-Object -Com Excel.Application

foreach ($File in (gci *xls)) {
$Workbook = $Excel.Workbooks.Open($File.FullName)
$Workbook.SaveAs($File.FullName.Replace(".xls",".csv"), 6)
$Workbook.Close($false)}

$Excel.Quit()