We consider a procedure for coarse-graining polymer molecules from the atomistic level of description to the reptation level for entangled polymers. The coarse-grained polymer model obtained with a competing-spring construction belongs to a class of models, referred to as tapeworms, for which a straightforward solution scheme based on generating functions is discussed and illustrated. The significance of the results and several perspectives for nonequilibrium simulations of entangled polymers are discussed. (C) 2004 Elsevier B.V. All rights reserved.