Microsoft is committed to support the vb6 runtime environment on Vista. However they will not continue to support the IDE: the development environment is not officially supported by Microsoft on Vista.
More detailed information can be found at:
VBRUN and ftponline
Additionally, do not forget to also verify the support of your third party controls. Are they being supported by their manufacturer?
Many companies have already moved or are in the process to upgrade their Visual Basic Applications to .NET. However, many others are procrastinating their decision. Which type are you? Dont'you think it is time to move yet? What are you waiting for?