Well it might be worth getting
OS 10.4, The Missing Manual as its a good primer in all things OS X.
In terms of other good sites, you're already here! Seriously, this board is friendly and there are many people ready to answer your questions. That said, there are some general guides that Looked ok. There was one on
the basic OS X software you get with the machine, but just
Googling for OS X switchers guide was pretty good.
Other specific sites that are good,
MacFixit for diagnostics and
Mac OS X hints for little hacks etc, but both of these are less generally helpful the macosx.com IMO.
To try and answer your more specific issues:
Your HD _should_ work, at lest for read only, as you seem to have been told, NTFS cannot be written to by any system but Windows as MS keep the system closed (linux users have the same issue). Let us know what you're tried so far and how the machine responded. Did anything appear on your desktop or in the sidebar of the Finder windows when you plugged it in? Did you get any pop up messages saying it couldn't be read? If you give us more info we can help you troubleshoot.
If you need a drive that can be read by both systems, eother use FAT and work aroudn the 2gb max file size or pick up
MacDrive which allows Windows to read and write to the HFS+ format that Apple uses for drives.
On how things are stored, I'm guess what's troubling you are the standard locations for things.
In the root folder of your hard drive, there are a bunch of folders, the only ones you need to know about are 'Applications', where applications available to all users of the machine are stored (there is another applications folder for things for one user only but it's not relevant for most people who are the sole users of their machine).
The other key folder is Users. In here you will find a folder with the name of the account you set up when you first started up the mac. For me its MyHDname/Users/ora. This is often refereed to as you 'home' folder, and where most things are stored. If you use the apple programs, then its all quiet self explanatory. iTunes keeps your music in the Music folder, iPhoto keep your pictures in the Pictures folder. The desktop is generally used as a temporary space to keep things, but is also a proper folder in your home folder, predictably called Desktop. Most people keep text files in the "Documents' folder.
I hope this is what you were after, else let us know and we'll work it out.