What version of Visual Studio are you trying to open it in? Visual Studio 2010 no longer supports conversion of pre-.NET VB projects, so you'll need an earlier version of Visual Studio to attempt a conversion.
The Upgrade tool that is included with Visual Basic .NET.
This happens automatically when you open a Visual Basic 6.0 project in Visual Basic .NET: the Upgrade
Wizard steps you through the upgrade process and creates a new Visual Basic .NET project (your existing project is left unchanged). This is a one-way process; the new Visual Basic .NET project cannot be opened in Visual Basic 6.0.
When your project is upgraded, the language is modified for any syntax changes and your Visual Basic
6.0 Forms are converted to Windows Forms. In most cases, you will have to make some necessary manual adjustments until the code is compliable after it is upgraded. This is required because certain objects and language features either have no equivalent in
Visual Basic .NET, or have an equivalent too dissimilar for an automatic upgrade. After the upgrade, you may also want to change your application to take advantage of some of the new features in Visual Basic .NET.