well, you would ahve to go out and get a modeling program. youll probably have to pay for it.
then you would have to learn to use it.
next you would make the model in it.
then you would skin it and compile
and the peter griffin you have would be very little use for a model, although you might be able to use its colors to see what to put where. but you could use it as a sprite.
and this shoud be in HL1 mapping questions not here.