Debtree generates dependency graphs for a specified package. The output is written to STDOUT and can be used as input for the command dot from the package graphviz ( a rich set of graph drawing tools ).
As root : apt-get install debtree graphviz
Usage : debtree package > out.dot create .dot file
dot -T png -o out.png out.dot create a graph ( PNG ) from a .dot file
Link : http://collab-maint.alioth.debian.org/debtree/index.html
Apt-rdepends is another tool that can create dot graphs.