This paper describes a process for the semi-automatic conversion of numerical and scientific routines written in the C programming language into Triana-based computational services that can be used within a distributed service-oriented architecture such as that being adopted for Grid computing. This process involves two separate but related tools, JACAW and MEDLI. JACAW is a wrapper tool based on the Java Native Interface (JNI) that can automatically generate the Java interface and related files for any C routine, or library of C routines. The MEDLI tool can then be used to assist the user in describing the mapping between the Triana and C data types involved in calling a particular routine. In this paper we describe both JACAW and MEDLI, and demonstrate how they are used in practice to convert legacy code into Grid services.