Wow. George Ou from ZDNet wrote yesterday about NASA's new supercomputer, the most powerful single node computer in the world. It comprises 1024 dual-core Itanium2 CPUs with 4Tb of memory.
The article doesn't say what OS the beast is running, but one of the comments says that they have used a custom kernel based on RedHat (since the standard kernel won't scale to that number of CPUs).
Since Windows is (still) available for the Itanium architecture, I bet it would be possible to run Win2003 or maybe 2008 on this box. It makes more economic sense, though, to have more servers running fewer CPUs and scaling "out" rather than "up"... but if you you could run Windows on this box, Solitaire really would fly :-)