When you create a project with Sitefinity, it creates an ASP.NET Web Site. As you may know, the ASP.NET 2.0 allows you to use different languages (C#, VB.NET) in one Web Site, so there is no problem to write your code in VB.NET and you don't need to configure anything.
Perhaps you have seen some C# code in the SItefinity site admin, but you don't need to change anything there. But yet if you have some problems understanding code written in C#, you can convert it using our C# <-> VB.NET converter
Hope this will help. Please let us know if you have additional question.