For the most part, if you are doing simple development projects, then the
Express products will handled them nicely. The individual Express products
are more or less the individual modules contained in VS 2005. What you
don't have in the Express products are all the bells and whistles that come
with VS 2005 Professional (Crystal Reports for .NET, full deployment
functionality, source control) and Visual Studio Team System (team
development features like code coverage and unit testing). Overall, though,
the Express products can produce the same base applications and libraries
that can be produced in VS 2005.
As for approaching your decision regarding which version to use, yes, if you
have a large enterprise development structure in terms of either a large
number of developers or a large amount of development projects, then the
full Visual Studio products are maybe what you need. Look here for a
comparison of the various VS 2005 editions:
http://msdn.microsoft.com/vstudio/products/compare/default.aspx