I wouldn't buy anything, I know Microsoft has its C++ compiler (7.1 I
think) freely available for download but it doesn't come with a project
manager (there are lots of alternatives to the Visual C++ project
manager).  I believe that Microsoft has also released cut down versions
of its next compiler technology with an IDE.  Then there's gcc and other
GPL/etc. compilers.

There's a difference between the latest C++ and the latest compiler
version.  C++ is a published language standard and few (if any)
compilers implement it fully (including Microsoft's compilers).  The
latest released Microsoft C++ compiler (the one in Visual Studio.NET
2003) is very close to the current language standard and gcc is too I
believe.  There's a new version of Visual Studio coming out soon (it's
in Beta) called Visual Studio .NET 2005 and it will have further
enhancements and probably even better standard compliance than the
current version.  I think that the new free IDE versions are based on
the up-coming compiler (they have similar names I believe).

.NET is a platform not a language.  So, while I believe it requires
extensions to C++ it is still C++ if you use a C++ compiler.

I don't know about the upgrade question but I believe that student
discounts do exist (plus consider the free versions Microsoft has
available).