Mono is an open-source implementation of the .net framework, which is what I think VB uses.
Monkeyguide - Mono

Probably you'll want to use an IDE. There are many options. Here are two:
Main Page - MonoDevelop
Welcome to NetBeans
How to install these will vary depending on which distro you end up using.

Many people are also fans of using emacs or vim for programming. Either Vi or vim come installed on pretty much every distribution.

Depending on your level of knowledge, probably one of the best ways to learn is to look at other people's code. This is one of the great strengths of open source software - you can easily do that.

F-Spot and Tomboy are two popular mono apps.

And some java info: Open Source Software in Java