Well, VB.NET utilizes the tools and classes available in the .NET Framework while classic VB does not target this framework.
While the syntax of the two languages are similar, the technologies are quite different. One of the most important differences that come to the top of my head are how the technologies handle problems: VB.NET uses Exceptions while classic VB doesn't. Another thing that comes to mind is how functions return values....VB.NET uses the "return" keyword while classic VB doesn't have this keyword available so you use the function's name (omitting the keyword "Call").
The two technologies manage memory differently as well. An Integer in VB.NET is not the same as a classic VB integer.
According to this article "
Support Statement for Visual Basic 6.0...", Microsoft support for VB classic IDE ended in April of 2008.
Unless you are maintaining a legacy application that has been implemented in VB classic, I recommend that you stick with VB.NET.
-Frinny