So, for all that I am pretty computer savvy, I have never dealt with networking before. I have 3 laptops that I use alone, plus a desktop and 2 laptops that are used by the rest of the family. We all connect to the internet using the same wireless, or wired router. The desktop is wired, the laptops are usually wireless. We also have a printer that I'm pretty sure has wireless capabilities, but I'm not even worried about that right now. My goal right now is to create a way to share files between my three computers, without allowing access to the rest of the house. I'm having some serious issues.

Computer 1: Dell Inspiron, Windows XP Home SP3, Odin
Computer 2: Toshiba Satellite, Linux Ubuntu Karmic, Thor
Computer 3: HP Pavilion, Windows Vista Ultimate SP2, Apollo

Apollo can can't make up his mind, and sometime will view files on Odin, sometimes on Thor, sometimes both, sometimes neither.
Thor can view files on Apollo, but not Odin.
Odin cannot view any other files.

Obviously, I'm doing something wrong. I think I just need to start over, but truth is, I'm flying by the seat of my pants here. Any progress at all was got by guesswork and 'just clicking on stuff', so I'm not sure where I *should* start... Any help would be greatly appreciated...

File sharing requires that you adjust or remove anything that would be blocking that type of access on the network. The typical program that causes intermittent file sharing issues like this is Norton Internet Security, but any firewall can cause problems and you need to look into what security software you have installed and determine if it has a firewall to block things.

As far as blocking file access from certain members of the household, you will have trouble doing anything like that with a "home" operating system. There is virtually no security on a "home" operating system (Windows XP Home, Vista Home, etc.). If you share a file or folder you share it with all.

Your main problem sounds as if you need to disable or re-configure your internet security, or firewall software though.