Вот решение VBScript.Не проверял, но это должно, по крайней мере, поставить вас на правильный путь.
Dim FSO, txs, fld, fil, content, nLinesToSkip, i
Set FSO = CreateObject("Scripting.FileSystemObject")
nLinesToSkip = 7
fld = FSO.GetFolder("C:\test\")
For Each fil In fld
If Right(fil.Name, 3) = "txt" Then
Set txs = fil.OpenAsTextStream(1) ' 1 = for reading
For i = 1 To nLinesToSkip
txs.SkipLine
Next i
content = txs.ReadAll
txs.Close
Set txs = fil.OpenAsTextStream(2) ' 2 = for writing
txs.Write content
txs.Close
End If
Next fil