Well for one no one uses Net Framework on a PC.. Unless your on a dedicated server or trying to convert a PC into a dedicated server you don't need framework. What it does is basically show how stuff should connect for certain server programs like for game servers. If VMK every makes the client use it then run like the world is on fire because there is no need to use Framework in a client.
You couldn't be more wrong. The Microsoft .NET Framework is, in simple terms, a runtime environment for applications written to run in it. Much like the runtime environments of Visual C++ and Visual Basic of the past, the .NET Framework is just an API set for managed-code applications. Think of it as JRE (Java Runtime Environment) on steroids. JRE is the same principle... an environment and set of APIs for applications written to run in JRE.
Newer Windows applications are being written in .NET for very good reasons. Visual C++ can compile unmanaged and managed code (managed code is the term used for code that runs in the Framework). Visual Basic.NET creates managed code. C#.Net creates managed code. All of the most popular languages in the Windows development world are now built around the Framework.
More and more applications off the shelf use the Framework. More and more websites are using newer standards that take advantage of the Framework (look up XAML sometime... some of the richest browsing you've ever seen is dished up using XAML, IE7, and .NET Framework 3.0.)
The Framework gives us developers a rich and static environment to code against, knowing that the same APIs will be available regardless of the platform on which it is running. It provides us better security tools, it provides us well-defined interfaces to do most anything we need to do, and does away with the whole mess of COM-based DLLs (ie 'DLL Hell'). No longer do we break other applications when we have a dependency on a newer system DLL that we must update!
Sure, the Framework is used on servers that host ASP.NET applications or WebServices, but the Framework is not a server-only environment.
And, just for the record... when you're asked to update and install .NET Framework 3.0, do it. It enables you to use the next generation of applications that will be built using the .NET Framework 3.0. Having the latest .NET Framework is a GOOD thing.