Oh, well, for every new model you want to put in, you have to add in a line of code for it in md2.dat. Here's what you put in:
(name of texture) (name of model) (size) (offset)
So if you want to put in a model for Blue Crawlas, it might be something like:
POSS POSS.MD2 3.0 0.0
(Note, the size is probably different. Play with that number until the model looks right.)