1. Its interface can have a steep learning curve for most, its powerful and customizable but it takes a lot of practice and patience to pick up. Mudbox has a better interface (though I don't like it that much)
2. You can make vehicles and architecture-but it will be pretty difficult, a new user such as yourself might find it pretty frustrating.
I would recommend trying to find a demo of Zbrush 2 and try that out, it interface is nearly exactly the same thing.