Posted by: Duncan Mackenzie, MSDN
This post applies to Visual Basic .NET 2002/2003 and Visual Basic 6.0
J. Henshaw asks "Is it possible to run both VB6 and VB.Net on the same machine,or do I have to remove VB6 to be able to use VB.NET", and the answer is a definite yes. You can run them both on the same machine.
Many people, including myself, run VB6 on the same machine as their installation of Visual Basic .NET. If you look at this KB article from Microsoft Support, you will even see that it recommended to run VB6 and VB.NET on the same machine when upgrading projects from one to another.
For more information on moving from VB6 to VB.NET, check out this page from the Visual Basic Developer Center.