Planning and performing a Visual Basic 6.0 migration is not that straightforward. You need to keep track of many small details, and you need to keep in mind the complete migration process – in other words, always see the big picture. The tool I posted about yesterday, the Code Advisor and the Assessment Tool, are invaluable in the help that they provide during the planning stages of the project. For the complete upgrade process, however I have to recommend the Upgrading Visual Basic 6.0 Applications to Visual Basic .NET and Visual Basic 2005 guide from the patterns & practices Developer Center over at MSDN.
This guide was written as a joint effort between Microsoft and ArtinSoft, and details all the steps necessary to succesfully upgrade your applications to Visual Basic .NET. It also deals with the actual technical hurdles you normally face when performing these types of conversions. Overall it is very comprehensive, and should be in your library if you ar planning or performing one of these projects.
If you are using the VB Upgrade Companion, and decide to upgrade to C# instead, most information from the guide still applies. That is one of the beauties of the .NET Framework – the concepts from VB.NET work with C# as well.