We propose a novel object-oriented design approach for developing a platform-neutral IP/TV presentation system for playing live TV-like MPEG video streams on the Internet multicast by RTP-compliant servers. Unlike proprietary viewers, such as Cisco's IP/TV viewers, which run only on Windows platforms, our system runs on any Java Virtual Machine environments. We demonstrate the effectiveness of our design approach via actual experimentations. We also propose a Java-based relay agent architecture for relaying RTP streams across multicast-enabled routers. We show that our system is particularly suitable to run as relay agents in this architecture to tackle the cross-platform issue and to accommodate various audio or video media sources efficiently. By adhering to the Internet and multimedia standards, our system is generically applicable to various media streaming systems.