08-24-2009, 11:42 AM
The things like Library appearing twice is quite normal. Library under the root folder (looking at the finder, it's the one that appears if you open Macintosh HD) are global preferences and settings for apps.
The Library that appears under your user name is your personal folder that contains data and configurations specific to your account. Things like Calendar Data, your personal configuration data for keyboard, mouse settings, mobile me information, etc.
Both Libraries supply specific functions, so you don't want to delete one of them thinking you don't need it.
There is a base file structure that OSX expects to see - beyond that you're pretty free to do what you want. As you're coming from a DOS/Windows environment, think of it as similar to windows in the that windows expects to find certain things in certain places and if you just go blindly removing or moving base folders/files or it can cause windows to not function correctly.
Basically - don't be moving or deleting files or folders unless you know what it may or may not do to your system.
Under your personal directory, feel free to add folders under Documents, Downloads, your personal home directory, etc.
If you want to get a better feel for the system, and haven't already gotten it, I strongly suggest you look into getting:
Amazon.com: Mac OS X Leopard: The Missing Manual (9780596529529): David Pogue: Books
as I think it'll really help your understanding of the OS. I saw it in a bookstore ages ago, and when I first switched to Mac, and was reading posts saw that it was highly recommended, and bought it and it has been a tremendous help in the switch.