As for C++ and .NET... there is no relevence at all.
C++ is a programming language, while .NET is a framework for languages to work within. .NET is closer to an OS than a programming language (but that is still a stretch).
C++ is similar to C#, which is essentially the .NET version of C/C++.
VB.NET and C# are similar in that they can do similar tasks. Their syntax IS different, but if you know one, you can learn the other one. O'Reilley publishes a number of books which give you a good idea of the differences.
Neither C# nor VB.NET are related to ASP.NET because ASP.NET is a web serving technology that can use either language, as well as several others like J# or some .NET flavor of COBOL, etc...
To understand the differences, look up what web servers do, what languages do, and then compare that against what .NET and the CLR are.
.NET comes out as something similar to Web Objects (now owned by Apple).