VB.NET has changed a little bit and is actually turning into a respectable programming language. However, learning VB6 isn't a complete waste.

Is it a better idea to pick up a VB.NET book? Depends, really. Do you want to make use of the .NET framework? Are you just learning programming to program? These are good questions to think about. But again, I think its a good idea to just continue what you are doing.