try this. You will probably need to play around with it to get it to fit your needs, but you can get the idea.
VB Code:
  1. Dim myBinary As New IO.BinaryWriter(System.IO.File.Open("D:\My Documents\binary.txt", IO.FileMode.Create))
  2.         Dim str As IO.Stream = myBinary.BaseStream
  3.         str.Write(Cases(0).XCoordinates.ToArray, 0, Cases(0).XCoordinates.Count - 1)
  4.         myBinary.Flush()
  5.         myBinary.Close()