I agree with this article about why bother?  Anyhow, the same article also
provided the solution to the funky problem with PowerPlus:  
http://www.adras.com/Add-Watermark-macro-Variable-not-defined.t7648-105.html

Here's recorded code that works to insert a picture, then it changes the
picture to a text watermark.  Of course, you need to plug in your picture
path.  The bottom line is that PowerPlus needed to be replared with the mso
language you will read about in the above article.

ActiveDocument.Sections(1).Range.Select
   ActiveWindow.ActivePane.View.SeekView = wdSeekCurrentPageHeader
   Selection.HeaderFooter.Shapes.AddPicture(FileName:= _
       "C:\Documents and Settings\Administrator\My Documents\My
Pictures\Glass1.jpg" _
       , LinkToFile:=False, SaveWithDocument:=True).Select
   Selection.ShapeRange.Name = "WordPictureWatermark1"
   Selection.ShapeRange.PictureFormat.Brightness = 0.85
   Selection.ShapeRange.PictureFormat.Contrast = 0.15
   Selection.ShapeRange.LockAspectRatio = True
   Selection.ShapeRange.Height = InchesToPoints(9.19)
   Selection.ShapeRange.Width = InchesToPoints(4.14)
   Selection.ShapeRange.WrapFormat.AllowOverlap = True
   Selection.ShapeRange.WrapFormat.Side = wdWrapNone
   Selection.ShapeRange.WrapFormat.Type = 3
   Selection.ShapeRange.RelativeHorizontalPosition = _
       wdRelativeVerticalPositionMargin
   Selection.ShapeRange.RelativeVerticalPosition = _
       wdRelativeVerticalPositionMargin
   Selection.ShapeRange.Left = wdShapeCenter
   Selection.ShapeRange.Top = wdShapeCenter
   ActiveWindow.ActivePane.View.SeekView = wdSeekMainDocument
MsgBox "added the picture"
   ActiveWindow.ActivePane.View.SeekView = wdSeekCurrentPageHeader
   Selection.HeaderFooter.Shapes("WordPictureWatermark1").Select
   Selection.Delete
   Selection.HeaderFooter.Shapes.AddTextEffect(msoTextEffect1, _
       "ASAP", "Times New Roman", 1, False, False, 0, 0).Select
   Selection.ShapeRange.Name = "msoTextEffect1"
   Selection.ShapeRange.TextEffect.NormalizedHeight = False
   Selection.ShapeRange.Line.Visible = False
   Selection.ShapeRange.Fill.Visible = True
   Selection.ShapeRange.Fill.Solid
   Selection.ShapeRange.Fill.ForeColor.RGB = RGB(192, 192, 192)
   Selection.ShapeRange.Fill.Transparency = 0.5
   Selection.ShapeRange.Rotation = 315
   Selection.ShapeRange.LockAspectRatio = True
   Selection.ShapeRange.Height = InchesToPoints(3.05)
   Selection.ShapeRange.Width = InchesToPoints(6.11)
   Selection.ShapeRange.WrapFormat.AllowOverlap = True
   Selection.ShapeRange.WrapFormat.Side = wdWrapNone
   Selection.ShapeRange.WrapFormat.Type = 3
   Selection.ShapeRange.RelativeHorizontalPosition = _
       wdRelativeVerticalPositionMargin
   Selection.ShapeRange.RelativeVerticalPosition = _
       wdRelativeVerticalPositionMargin
   Selection.ShapeRange.Left = wdShapeCenter
   Selection.ShapeRange.Top = wdShapeCenter
   ActiveWindow.ActivePane.View.SeekView = wdSeekMainDocument
   
   MsgBox "deleted the pic and changed to text"