Microsoft Interop Forms Toolkit

The Interop Forms Toolkit is a free Visual Studio add-in that simplifies the process of displaying .NET forms and controls in a Visual Basic 6 application.

Instead of upgrading the entire code base, these applications can now be extended one form at a time. The goal is a phased upgrade, with production releases at the end of each iteration containing both Visual Basic 6 and Visual Basic .NET forms running in the same Visual Basic 6 process.
Most importantly, the Toolkit guides you down a migration path that allows you to focus on writing code that adds business value instead of infrastructure and interop code.