Installing Rgraphviz:

The Rgraphviz package requires a bit of extra work beyond 
simply installing the package itself to run properly.  The user
must first have installed the GraphViz software provided by AT&T.
For users of the release version of Rgraphviz from Bioconductor 1.3,
this must be Graphviz version 1.10.  For users of Rgraphviz for
Bioconductor 1.4 (or the devel versions leading up to the 1.4 release)
this must be Graphviz version 1.12.

To do this:

- Go to http://www.graphviz.org/pub/graphviz/
- Download GraphViz.  NOTE: Please download the source
  and build using the sources instead of using RPMs or other prepackaged
  methods.  
- Unpack the distribution
- In the GraphViz directory, run './configure', 'make' and finally
  'make install'.  If you have special configuration needs, specify
  them with the './configure'.

Finally, make sure that you have the 'graph' R package installed.  

Once these things are both installed properly, you can then proceed
to install Rgraphviz.