1. Visual Basic 2003/2005/etc are VB
2. You can teach yourself VB
.NET with the right resources. There are lots of tutorials online. You can also access Wrox's online book library
for lots of their beginner books on VB
3. The .NET framework has extensive support for database access. All .NET languages can use those capabilities.
4. .NET doesn't have prebuild capabilities such as point of sale bill printing, that will be up to you to create. However, there may be third party applications or tools that provide that kind of functionality.