its certainly not a prerequisite - although the transition from no programming knowledge to learning VB.NET is certainly harder than the transition for an experienced VB programmer to VB.NET!
Whether to learn VB or VB.NET depends on your reason for learning the language - at the moment, VB probably has more use in a commercial sense; VB.NET is still too new. But if you're looking to the future, then VB.NET/C# is where its at!