Tradeoff analysis is a central aspect of any design process. Languages and tools to support performance modeling and tradeoff analysis are necessary to facilitate rapid prototyping of designs. An effective modeling and evaluation environment reduces the overall design time of both the prototype and the final product by helping designers in determining which parameters of a design are critical for meeting a set of desired performance goals. This paper describes a case study in performance modeling using a language called PDL (Performance Modeling Language). The PDL system supports tradeoff analysis and performance visualization. This paper also addresses some of the key issues for successful tradeoff analysis during rapid prototyping and explains how many features of PDL make it a suitable choice for this purpose.