Most of the stuff I've seen has been in C# rather than VB - but it will translate over very easily.
Have a look
here[
^]
It should give you the basics.
Then try MSDN for full details on the System.Speech.Recognition namespace.
Good luck - you hopefully won't need it!
[edit]They don't mention it, but you will need to add a reference to "System.Speech" and a "using System.Speech.Recognition;" before VS will understand you... OriginalGriff[/edit]
[edit]RT: Fixed link[/edit]