Not exactly sure what you mean and might well be going off on a tangent but
VB 2008 is VB.net, its just the 2008 release of Visual Studio. The naming of Microsoft development products is very confusing. but since VB6 all VB is VB.net.
There are three version that are a factor of this:
The visual studio version
The language version
The .net framework version
Each version of the above has its own functionality:
visual studio version – changes to editor tools, and refactoring tools in visual studio
language version – changes to what you can validly write as code and how it will be compiled
.net versions – changes to features of the run time and the standard set of .net classes and types available for use in compiled code
substring is a method of string – a .net type. its available in all .net versions and can be used by any language compiled to IL – the language that all “.net” languages compile to (e.g. VB.net ,C#,F#,IronPython etc.).
See here and check the other versions option near the top of the page:
You can use the MSDN to check anything you are wanting to use to ensure its compatible with the version of .net etc that you are using.