On the entry form Autodesk asks what other software you used in addition to Max. I don't know if plug-ins are allowed or not, but I'll bet they'll give more points to a team that modeled their own trees vs. teams that used a plug-in.
Here are some more tree tutorials. Some are not specifically done in Max, but the same principals apply:
http://www.andyzibits.com/tut_low_poly_trees.html
http://reinerstileset.4players.de/ha...d_3d_treeE.htm
http://bk-coffeehouse.cottages.polyc...timetree1.html
http://www.vterrain.org/Plants/Create/index.html