If you wanted to find someone good at VBA, you have come to the right place. VBA is a related to VB6, so there's no need to make a clear distinction. The major difference is that VBA is typically hosted by an office application such as Excel, and VB6 programs are usually stand-alone applications that can be run on their own. If you want to program Excel, VBA is a great tool for the job.
VB.NET would be helpful for Excel programming if you are planning on using VSTO (Visual Studio Tools for Office). I believe you could use another .NET language, such as C#, just as readily in this case. As Rorya said, we're likely to see more of this in the future - Microsoft seems to be investing in VSTO in order to bring .NET development tools into the office programming environment.
To sum up, both VB/VBA and VB.NET are excellent choices for Excel programming - you won't go wrong. It really depends on where you want to start out. If you want to work with Excel immediately, choose VBA. If you want to learn Visual Basic generally, then it hardly matters - just dive in.
Alex