Go here and watch the tutorials on all three molecules
http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom5s2_6.swf
then look at http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Sigma-and-Pi-Bonds-858.html
http://library.thinkquest.org/C0110275/
http://www.teachtheteachers.org/projects/GNiles/index.html
http://www.1001-periodic-table-quiz-questions.com/quiz/k-12/change_1.html
http://neon.chem.ox.ac.uk/vrchemistry/vsepr/intro/vsepr_splash.html