To download the files, you can do this:
Dim linkdl As String = "http://s3.amazonaws.com/MinecraftDownload/"
Dim filepaths As String() = New String() {"minecraft.jar", "jinput.jar", "lwjgl.jar", "lwjgl_util.jar", "windows_natives.jar"}
For Each filePath As String In filepaths
Dim webClient As New WebClient()
webClient.DownloadFile(linkdl & filePath, dirminecraft12 & filePath)
Next
More about the
WebClient.DownloadFile method[
^]
Hope this helps.