I am Brian Foley, PhD.
The organism I work on, the primate immunodeficiency viruses which include HIV-1 HIV-2 and SIVs, is not an official model orgamism. However, it should be model organism for many reasons. No other organism has as many isolates sequenced and classified as HIV-1 (we have genetic sequences from over 140,000 isolates as of April 2008). And we also know a lot about the epidemiology and geographic spread of HIV. It evolves very fast, and we have data covering over 25 years of evolution.
You can contact me at btf(at)lanl(dot)gov