This is another of those parallel developments that seem to be occouring so much lately.
Boo is a Python-like language for the .NET Framework.
IronPython is an implementation of Python on the .NET CLR
Boo is a great dynamic language for experimenting with .NET classes interactively, especially using the booish shell. The big adavantage of boo over c# is the lack of a compile step. This allows for editing of a running application. Boo does not yet support Generics (but this is being worked upon). Boo workings with .Net 1.1. .Net 2 and Mono.
IronPython is the first dynamic language added to the CLR family by microsoft. It is intended to demonstate that the CLR can support dynamic languages. IronPython requires .NET 2.0.