Would it be a good idea to start converting forms into .NET one at a time which you would then invoke from the VB6 app via COM-interop.
This way, by the end of the process you would just convert the 'shell' of the VB6 application into a new .NET app, and all your forms are ready to go in .NET.
Is there a better strategy?
We have a VB6 application which is being ported to .NET either, and we use the COM-Interop strategy. All new features can be implemented in .NET, only the GUI-stuff remains VB; at the same time, we can develop a new GUI independently.
If you don't already know this, you can do COM Interop without using the registry (as this caused some problems for us) with Registration-Free COM Interop: