Frequently engineers have useful but out-dated applications. This "legacy code" is often text-based, very often written in (some version of) Fortran, and much less than user-friendly. Such programs can be converted to run in an MS Windows environment to satisfy customers' requirements for a flexible, modern way of interacting with the underlying program. A PC Windows version of the program performs the same engineering calculations as the previous mainframe version written in Fortran. The purpose of the thesis is to design a practical graphics user interface for the Fortran legacy code program and to come up with some general guidelines on how to deal with legacy code problems. Visual Basic, a very user-friendly language tool, was chosen to implement the graphical user interface (GUI) for this project. The GUI characteristics of the project are described. Some advanced technology of Visual Basic, such as file handing, data access and manipulation, communication with Fortran, and Fortran output display, is also discussed in detail.