Some Delphi Questions.

Hi there,
        I'm currently working on a Delphi application. And i'm facing some
problems.
Hopefully, someone out there can solve/answer my questions.

1) Instead of using the structured way of programming, i've opted to use
the OO apporach. Using this approach, as far as i know can be in the form
of Unit files or Componenets. As yet, i dun need to write my own
components. Therefore, Unit files seems to the the only way out. I've not
seen any examples of defining classes in Unit files incorporating the use
of Delphi components.(visual or non-visual). Anybody has any idea/example
to share?

2) I'm using a TreeView component. My Tree has already been populated. I
would to select a node and then display the relevant node's details. I've
tried using GetNodeAt(which requires the mouse position coordinates).
However, it doesn't seem to work, Whenever i click a node, it will raise an
exception. Anyone with a better solution or able to solve my problem will
be greatly appreciated.

Thanks for taking the time to look through my questions.