In a recent discussion, the subject of grid computing came up. If you’re into it, you probably know about Digipede, which is a company based in Oakland which provides libraries which allow you to create massively parallel programs in .Net . Digipede allows you to set up a small two node cluster for experimentation purposes, but more nodes cost money.  

There is however, an open source project called Alchemi, which has a programming model which is very, very similar to Digipede, but is open ended and free. I run Alchemi on my home network and have had good success with it.

Also, of course, there is MS Compute Cluster server, which is a canonical implementation of MPICH on the MS platform (and in my experience is fairly difficult to integrate into .Net):

http://www.microsoft.com/technet/ccs/overview.mspx

Also of interest, although not specifically grid computing, is the Cω research language from MS research, and its asynchronous methods :

http://research.microsoft.com/Comega

http://en.wikipedia.org/wiki/C%CF%89  

http://research.microsoft.com/comega/doc/comega_tutorials_concurrency_extensions.htm