The .NET Server line of operating systems currently includes four different versions, three of which correspond almost one-to-one to the Windows 2000 Server, Advanced Server and Datacenter versions.

Windows .NET Web Server
This is a new version that does not correspond to any version of the Windows 2000 line of operating systems. It is meant to be used as a dedicated Web server for hosting applications and Web services. Since this is the low-end configuration of the .NET Server, it is limited to servers with either one or two CPUs and up to 2GB of RAM.

Windows .NET Server
This is the upgrade to the Windows 2000 Server version and it is intended as a general purpose file server, printer server, Web server, etc. It is limited to servers with up to two CPUs but can support up to 4GB of RAM.

Windows .NET Enterprise Server
This is the upgrade to the Windows 2000 Advanced Server version and it is for use by enterprises of any size as a high-end server. It can support servers with up to eight processors and with up to 32GB of memory (on x86-based servers) or up to 64GB on Itanium-based servers.

Windows .NET Datacenter Server
This represents the ultimate offering, in terms of both performance and reliability, and is the upgrade to the Windows 2000 Datacenter product. It will only run on servers with at least eight processors, but it can support configurations with up to 32 CPUs. It can support up to 64GB of memory on x86-based servers, or up to 128GB on Itanium-based servers.

Note that the supported configuration limits for all four versions may or may not change before the official release of the operating systems, but you can at least use them as a guide as to what to expect from each version.