Ever since I got my PC, I've tried to set up a network so that I can share files to another PC (with restricted access to certain files and folders). These attempts have always failed, and I am in a "do it yourself" mood, so, where do I start?

Here's where I'm at: I've got 3 PC's I want to connect, a laptop and 2 desktops. The laptop is running XP Home, while the desktops are both running Vista, one Home Premium, the other Ultimate. The PC running Ultimate is mine. The other two belong to members of my family. The laptop is intended just for using the printer attached to my PC, while the other desktop is intended for mainly the transferring of files inside a specific folder. Before you say anything else, I just want one question answered: