I don't have an FT to test this with, but I think this will be a start:
Dim request As FtpWebRequest = CType(WebRequest.Create("ftp://www.server.com/"), FtpWebRequest)
request.Method = WebRequestMethods.Ftp.ListDirectory
request.Credentials = New NetworkCredential("username", "password")
Dim response As FtpWebResponse = CType(request.GetResponse, FtpWebResponse)
Dim responseStream As System.IO.Stream = response.GetResponseStream
Dim reader As System.IO.StreamReader = New System.IO.StreamReader(responseStream)
Dim names As String = reader.ReadToEnd
reader.Close()
response.Close()
Dim FileList() As String = names.Split(New Char() {Chr(13), Chr(10)}, StringSplitOptions.RemoveEmptyEntries)
Array.Sort(FileList)
Dim NewestFile As String = FileList(0) '*May be FileList(FileList.Length-1)