Refer to the Silk Central Release Notes to ensure that you have the appropriate SDK version installed and in your PATH.
It is helpful to have the JUnit jar in your classpath. You can download the JUnit.jar file from http://www.junit.org/index.htm.
wsimport -s <path where to save the generated files> -Xnocompile -p <package structure you want to use for your client yourWebService> http://<URL to your service>/yourWebService?wsdl