There are a lot of similarities between VB.NET and VB 6 but there are also many differences. The VB.NET syntax will seem familiar to a VB 6 programmer but there will still be a reasonable amount to learn before you will be able to feel comfortable in the .NET environment. One of the most important differences is that VB.NET is a proper object oriented language, which can be one of the main stumbling blocks for some users of previous VB versions. If you aren't well versed in OOP, you should start by doing some reading on the subject. If your dad is using Visual Studio .NET then he should be able to help you out. Even if he has been using a different VS language, like C# for instance, the OO concepts are the same.
I recently switched from VB6 to VB.NET, at first it is really different. Try to start again with the "Hello world" program and download a few code samples, then you'll realize that it's not really that different.