Turn on Personal File Sharing in System Preferences>Sharing on one (or either) computer, then from the finder go to Networks, click on the name of the computer on which file sharing is enabled, and you'll be able to transfer files back and forth using the Drop Box (and the Shared folder).
Yes, once you've enabled file sharing on one or both macs, you can use the shortcut "command + K" in Finder. Then you type in the ip adress of the mac you want to access, and the password, and there you have it
I have a network of 11 macs, 9 of them wireless, using an airport extreme base station, and 2 wired, and it works perfectly
You can also then share printers, music, videos photos etc as well