Increase your generic High Performance Computing smarts

Many new Windows HPC Sysadmins will be heading in from the Enterprise, having expertise in Microsoft platforms but relatively little knowledge of HPC. This is certainly the route I took, having worked in large enterprise (50K+ users) in previous roles.
The good news is that Windows HPC Server is built around standard, common, Microsoft (and other) technologies. If you have good knowledge of Active Directory, Windows Deployment Services, Windows Server, data storage and the like then you've got at least the platform component of the cluster under your belt.
The flip side is that HPC demands knowledge of technology which is rarely used in the enterprise world. Primary amongst those is Message Passing Interface (MPI), a protocol which is used extensively for distributed memory type jobs running across multiple compute nodes. While it's possible to maintain a Windows HPC cluster without in depth knowledge of MPI, from experience I can say that the time spent learning about how this area works is a very worth while investment. If I had to specify the information I've found most useful in this area it would be knowledge of process placement and affinity.
I've also found that a little knowledge of non Windows HPC technology is useful. There are some very interesting and innovative solutions out there.
I use a couple of HPC specific news sites on a semi regular basis:
http://insidehpc.com/
and
http://www.hpcwire.com/
These are informative, and give an overview of trends and developments in the field.