The 2nd release candidate is now available for beta community participants. You can download the bits by registering as a beta participant at http://connect.microsoft.com. See the "Windows HPC Server 2008 beta program".
A significant new feature with RC2 is the ability to schedule jobs using applications designed to offload processing to multi-core graphics cards. A white-paper published within the beta program downloads section details this feature. A typical command line to submit a graphics processor job uses the new HPC_ATTACHTOCONSOLE environment variable as follows: “Job submit /env:HPC_ATTACHTOCONSOLE=TRUE mygpgpu.exe”
Graphics processor offload for HPC workloads is an area of very active research and development. See the Microsoft Research Accelerator project and the recent Sandia Labs "Roadrunner" entry in the Top500 along with a very "geeky" but interesting project at the University of Antwerp.