Having never programmed .NET, I am pretty ignorant on the subject. But, what little I have read leads me to think it's something along the lines of what Borland did with its VCL a LOOOOooong time ago: an easier-to-use set of libraries, objects, etc. which make Windows programming faster, safer and more reliable than coding straight in the API. The VCL could be deployed as run-time BPLs (Borland's DLLs) or linked in for a single-file executable.
Of course, the VCL is not as multi-lingual as .NET appears to be, so there are certainly differences. But isn't that basically what .NET does: provide a framework and huge library to simplify Windows programming?
Am I completely off base?
It can be used that way. Some of .NET is a wrapper around the old Windows libraries, especially if you're using Windows Forms and other underlying standard APIs. Microsoft also suggests programming in .NET instead of the old ways like MFC.
But .NET is technically platform agnostic. Others have written the framework for other operating systems, allowing .NET apps to run on them. In this way it's like Java.