Right, first let me say you are on the right track. Visual NHibernate has come a long way from a tool to generate NHibernate Mappings and Classes from just Microsoft SQL Server to a tool that does all the major Databases (I am biased cause it does MySQL now).
Like the name suggests, it doe the configuration setup visually with a rather tasteful (lately) UI (Probably WPF) that surprisingly does not tax your computer!! It also allows for setup of validation rules, Auto-detection of relational integrity (Primary - Foreign Keys) and all this with a very very flat learning curve.
If you use Oracle, Microsoft SQL Server or MySQL Server and you do not wish to spend too much time designing mappings and typing classes then this is the tool for you.