We describe: (i) the architecture of an optical burst switched (OBS) demonstration network overlaying the ATDnet transparent all-optical testbed, and (ii) experiments underway in the testbed. The OBS overlay uses a simple hardware-based protocol embedded in OBS network controllers to manage commercial off-the-shelf DWDM switches. Data paths are all-optical and completely transparent, and can carry analog or digital traffic in any format, data rate, and modulation scheme. Experiments with latency- and jitter-sensitive HDTV transmission, petabyte file transfers, and immersive real time visualization of satellite imagery over the OBS network are ongoing. Parallel research on transport protocols, QoS-aware routing protocols, adaptors for an OBS LAN, and network management architecture are applied as completed. This is the first just-in-time (JIT) OBS field trial known to the authors.