Microsoft Visual Studio .NET Enterprise Developer (and Microsoft Visual Studio .NET Enterprise Developer Upgrade) supplements the core Visual Studio suite with a copy of Windows .NET Server (licensed for development and testing), which means this package provides the infrastructure you need to actually publish Visual Studio .NET applications. The Enterprise Developer edition also supports integration with team software development environments--particularly Microsoft Visual SourceSafe 6.0. Such environments manage versions of software in development and enable groups of programmers to efficiently share development responsibilities.
Microsoft Visual Studio .NET Enterprise Architect (and Microsoft Visual Studio .NET Enterprise Architect Upgrade) really shows off the promise of the .NET application architecture. With the Enterprise Architect edition, application designers step back from the coding a bit and instead use Unified Modeling Language (UML) to describe--in abstract and language-independent terms--what objects will compose an application, what properties and methods they will have, and how they will interact. Other tools enable the architect to define coding templates and design policies for use by more junior members of a programming team (adherence to published templates and policies is enforced by other Visual Studio .NET environments on the corporate network). Of course, few software architects want to keep their hands totally clean of coding work, so the environment provides all the development tools of the lesser Visual Studio .NET products as well.