...

Do you?  I don't see it.  A question would usually be followed by
a question mark '?'.  The question marks denotes a question.  It
also helps the reader to quickly identify the question in usenet posts.
I encourage the use of one (approrpriately applied) question mark in
each post.

Why PBM?  I had to google to find that was some sort
of monochrome (ick) image format.

Why not save as PNG?

Here are two methods from the WebStartFrame I am developing.
They might get you started..

 public static BufferedImage getScreenShot(
   Component component) {

   BufferedImage image = new BufferedImage(
     component.getWidth(),
     component.getHeight(),
     BufferedImage.TYPE_INT_RGB
     );
   // call the Component's paint method, using
   // the Graphics object of the image.
   component.paint( image.getGraphics() );
   return image;
 }

 public void saveScreenShot(BufferedImage image) {
   getLogger().log(Level.FINEST, "Default saveScreenShot");
   try {
     ByteArrayOutputStream baos = new ByteArrayOutputStream();
     // write the image as a PNG
     ImageIO.write(
       image,
       "png",
       baos);
     byte[] bytes = baos.toByteArray();
     ByteArrayInputStream bais = new ByteArrayInputStream(bytes);

     saveFileDialog(null, null, bais, null);
   } catch(Exception e) {
     handleError(e);
   }
 }