what's the story on dot?

What did I miss doing? I read the README. I built Synopsis using
     python setup.py build

And now I see
[email protected] [~...hermes/qstore] 107: synopsis -p Python -f 
HTML -o ~/GCQ gcq.py
dot: not found
Traceback (most recent call last):
   File "/usr/local/bin/synopsis", line 182, in ?
     main()
   File "/usr/local/bin/synopsis", line 179, in main
     processor.process(AST.AST())
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Processor.py", line 
165, in process
     ast = self.processors[-1].process(ast, **my_kwds)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Formatter.py", 
line 183, in process
     view.process(start)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Views/Scope.py", 
line 74, in process
     self.process_scope(ns)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Views/Scope.py", 
line 115, in process_scope
     part.process(ns)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Parts/Heading.py", 
line 41, in process
     decl.accept(self)
   File "/usr/local/lib/python2.2/site-packages/Synopsis/AST.py", line 
446, in accept
     def accept(self, visitor): visitor.visitClass(self)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Part.py", 
line 149, in visitClass
     def visitClass(self, decl): self.format_declaration(decl, 'format_class')
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Part.py", 
line 127, in format_declaration
     type_name = map(format, self.__formatdict[method])
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Part.py", 
line 125, in <lambda>
     format = lambda func, decl=decl: func(decl)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/HTML/Fragments/ClassHierarchyGraph.py", 
line 41, in format_class
     title=label)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/Dot.py", 
line 508, in process
     _format_html(tmpfile, self.output, self.base_url)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/Dot.py", 
line 407, in _format_html
     _format_png(input, output + ".png")
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/Dot.py", 
line 398, in _format_png
     def _format_png(input, output): _format(input, output, "png")
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/Dot.py", 
line 396, in _format
     system(command)
   File 
"/usr/local/lib/python2.2/site-packages/Synopsis/Formatters/Dot.py", 
line 41, in system
     raise SystemError(ret, command)
Synopsis.Formatters.Dot.SystemError: SystemError: 7f00"dot -Tpng -o 
"/home/vlbrown/GCQ/Scopes/gcq/QueueError-inheritance.png" 
"/home/vlbrown/GCQ/Scopes/gcq/QueueError-inheritance_html.dot"" 
failed.
[email protected] [~...hermes/qstore] 108:

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