Program for computing Tree decomposition of a graph
Some of these software might help you. (Not all of them are open-source though.)

*TreeD http://www.itu.dk/people/sathi/treed/

*dlib http://dlib.net/

*QuickBB http://www.cs.washington.edu/homes/vgogate/quickbb.html

*Hypertree http://www.dbai.tuwien.ac.at/proj/hypertree/downloads.html

*LibTW http://www.treewidth.com/treewidth/