In some migration projects you have to take an incremental approach. You just can't disappear with an application for a few months, and then come back with the application in the target language. Because of this, when we do migration projects, we try to divide the project in smaller milestones, so that developers can continue working on a certain module of the application, while another group migrates a different module.
It turns out that is you are migrating from Visual Basic 6.0 to the .NET Framework (using either Visual Basic.NET or C#), you can do even smaller steps. Microsoft offers the Microsoft Interop Forms Toolkit, a set of tools that you can use to run .NET forms and controls in VB6 applications. This Toolkit allows you to create an even less disruptive migration strategy, by creating an incremental upgrade process in which you can start out by moving some controls first, then some forms, and, before you know it, you'll have your applications running completely in .NET.
I realize this has been out for a while, but it is still worth mentioning, since there's tons of people out there that haven't moved from VB6 yet. This may give all of you some incentive to at least get started with the first incremental steps. :)