You'll have to override the scrollable increment methods in your
scrollable component (the thing you add to the scrollpane). Following
code makes scrolling in a JEditorPane really slow. The numeric values
are the number of pixels the view should be moved for a click on the
arrow or in the gray area of the scrollbar.

JEditorPane ePane = new JEditorPane(url) {
   public int getScrollableUnitIncrement(Rectangle visibleRect, int
orientation, int direction) {
       return 1;
   }

   public int getScrollableBlockIncrement(Rectangle visibleRect, int
orientation, int direction) {
       return 2;
   }
};

Regards,

Bart

JScrollBar.setUnitIncrement