Sam,

Only one problem - you cannot use 600 columns on one sheet.  But you can put the data onto separate
sheets: the code below will put data from 100 files onto each sheet.  Run the macro below, and
select the files that you want to process.  (I'm not sure if there is an upper limit on the
multi-select feature of the workbook open dialog, but you can always do this in multiple batches.)
Note that this may take a loooooong time, depending on file size, since you are opening and closing
600 files.

HTH,
Bernie
MS Excel MVP

Sub OpenMultipleUserSelectedFiles()
Dim filearray As Variant
Dim mySht As Worksheet
Dim i As Integer

Set mySht = ThisWorkbook.ActiveSheet

filearray = Application.GetOpenFilename(MultiSelect:=True)
If IsArray(filearray) Then
  For i = LBound(filearray) To UBound(filearray)
     Workbooks.Open filearray(i)
     Range("B28", Range("B28").End(xlDown)).Copy
     If mySht.Range("IV1").End(xlToLeft).Column > 100 Then
        Set mySht = ThisWorkbook.Worksheets.Add
     End If
     With mySht.Range("IV1").End(xlToLeft)
        .Cells(2, 2).PasteSpecial xlPasteValues
        .Cells(1, 2).Value = filearray(i)
     End With
     ActiveWorkbook.Close False
  Next i
Else:
  MsgBox "You clicked cancel"
End If
End Sub