What precisely do we mean by ASP.NET version 2.0 ? Is it the version lined with .net CLR version 2.0 ?
What about aspnet_isapi.dll and aspnet_wp.exe ? How do they fit in with respect to the versions 1.1 / 2.0 / 3.5 of the .net framework?
.NET 3.5 uses CLR 2.0. Does that mean nothing changes in ASP.NET 3.5 except for additions to the Class Libraries ?
ASP.NET 2.0 is the framework that shipped with .NET 2.0 (and thus CLR 2.0). In most ways, this number currently aligns most closely with the CLR version, in that although .NET 3.0 / .NET 3.5 add extra assemblies that can (and are) used by ASP.NET applications, there is no new ASP.NET version number.
Re your last point... "nothing changes"... well, the code that runs is largely dictated by the class libraries. So; yes, there are new dlls, and minor tweaks to the older dlls. But indeed, the core technology itself remains more or less the same.
ASP.Net indeed uses the CLR 2.0. This also means there is a seperate aspnet_wp.exe running. SO if you have both 1.1 and 2.0 asp.net sites running you'll see two aspnet_wp processes in the task manager.
On top of that there are several new features for asp.net 2.0. Some stuff I can think of includes Master Pages, styles, better controls, split up view state/control state, improved compression of viewstate and much more
3.5 uses CLR 2.0 so there is no difference in worker processes used.
For all info: check the asp.net site: http://msdn.microsoft.com/en-us/asp.net/default.aspx
There are a lot of differences between ASP.NET and ASP.NET 2.0. The .NET Framework page on wikipedia is actually pretty good at describing how the Framework has evolved from 1.1 to 2.0 to 3.0 to 3.5 and it will be 4.0 soon. :)
ASP.NET 2.0 is simply an ASP.NET application running under the 2.0 CLR. This is configured in the properties for the application in the IIS manager.
Applications that target framework 2.0, 3.0 and 3.5 runs under the 2.0 CLR. The CLR is (except for a few breaking changes) backwards compatible, so an application targeting framework 1.1 can generally also run under the 2.0 CLR.
Each application pool in the IIS can only use one CLR version, so all applications in a pool has to either use ASP.NET 1.1 or ASP.NET 2.0. If you try to mix CLR versions in an application pool, the sites in the pool will stop working.