Phylogeny and systematic has become a key component of the Option D: Evolution, with the revision of the curriculum 2009 and its introduction in HL. However unless you studied Zoology at University the topic may be rather new to you.
Needing to feel grounded in the topic myself I very recently purchased The Nature of Diversity An evolutionary Voyage of Discovery by Daniel R. Brooks and Deborah A. McLennan. Though I have not read beyond the opening few pages the comprehensive nature of the text assures me I will become an expert by the end of the summer.
You may also wish to watch the following lecture from Yale University or watch the whole series on evolution and ecology.
I introduced the topic with the video narrated by David Attenborough from the Tree of life website, (very neat interactive here)
I showed my students the video How do we know where mammals come from? That’s on blip.tv. to give them a sense of how useful phylogeny can be for classifying organisms.
There is a neat interactive website “what did T-Rex taste like?” that your students could explore.
And lastly there is the following W2_buildatree that you could do as a class exercise with GenBank® (an NIH genetic sequence database, an annotated collection of all publicly available DNA sequences (Nucleic Acids Research, 2008 Jan;36(Database issue):D25-30)) though this exercise is rather complex.
Hope this helps.