I assume that you're working on XP, right?

On either machine open explorer and create a directory called 'Share' can be anything you want it to be.

Right-click\properties\sharing

Click 'Share this folder' and then click permissions

On the bottom part of the dialogue you should click Full Control, so that 'Everyone' has full control.

This should ALWAYS only be done on a private network behind a router firewall (if it has internet access)