There are some C# to VB.NET converters available. I've yet to see one that delivers 100% fidelity on the conversion, they are often adequate for most jobs. Here are two: both of them have discussions on their limitations and assumptions.

Clarity Consulting has a C# to VB.NET Converter that can be used online or downloaded.

Kamal Patel, Microsoft MVP, created ConvertCSharp2VB which can also be used online or downloaded.

Contributed from George Shepherd's Windows Forms FAQ