As others have said, for the most part, VB.NET and C# are essentially the same language just using different symbols/word for the syntax. You can use tools SharpeDevelop like http://www.icsharpcode.net/opensource/sd/ to switch your code between VB and C#
The only real down side to VB.NET is that it is considered the poor cousin to C#, mostly as it got its syntax from VB6 originally.
I would say that you should learn C# for a few reasons.
1) More jobs for C# than VB.NET
2) Most people work in C# in preference to VB.NET so easier to find help
3) Supported in Unity should you go that route.
4) Syntax is more terse so there is less noise in your code
5) Unsafe gives access to more "low level" stuff should you need it
6) There are many other C style languages out there and this will ease you into them
If you know VB.NET you know C# you just need to get used to reading and writing it