Well, you can buy either the full Visual Studio 2005 (which let's you
program in any of the 4 .NET languages) or you can buy a version of VS.NET
2005, that allows you to work in just one of the languages (in this case
VB.NET). It's like the difference between buying MS Office or just buying
Word.
But, after looking at the link you provided, I have to say that it looks
like what they are selling is just lessons on working with the VB.NET (the
2005 version). They are not selling the actual .NET software, just lessons
on using it.
If I were just to say VB.NET to you, you wouldn't know whether I meant the
2003 version (which is still widely used) or the 2005 version of the
language, which has some new features 2003 doesn't have. So, when people
talk about VB.NET, they ususally throw the year on the end to let others
know what, specific version they are talking about. When the year is not
attached, it is generally because people are just talking about VB.NET in
general.