You can't. If you want to orient your text differently then you'll need to draw it using GDI+. GDI+ drawing is done on the Paint event of the control you want to draw on. This will draw text vertically on a form:
vb.net Code:
  1. Public Class Form1
  2.  
  3.     Private Sub Form1_Paint(ByVal sender As Object, _
  4.                             ByVal e As PaintEventArgs) Handles Me.Paint
  5.         e.Graphics.DrawString("Hello World", _
  6.                               Me.Font, _
  7.                               Brushes.Black, _
  8.                               10, _
  9.                               10, _
  10.                               New StringFormat(StringFormatFlags.DirectionVertical))
  11.     End Sub
  12.  
  13. End Class
You should read the documentation for the Graphics class, it's DrawString method and the StringFormat class, then experiment to see what else you can do.