I'm on loop 3 and it seems madwifi-ng is already installed..
Anyway, I'll assume you have an older version which perhaps doesn't or something. To do what he said: install it / upgrade it if it's currently installed and has a new version in one of two ways:
GUI style: You can run kuroo, which you can find in the start menu under "system". Search for madwifi-ng in the upper right *NOTE: if its icon shows up green, you already have it installed.. check the bottom to see if perhaps there is a new version*. Next, add the madwifi-ng (and probably madwifi-ng-tools too couldn't hurt) to your queue (bottom button), then click queue over to the left, click "check installation" and go find something to do for a few minutes.. come back, if it's "done", click start installation, then go find something to do for a while. Come back in maybe 15 minutes, and it might be done, or it might be sooner or later. Notifications in kuroo are at the bottom left of the program.
OR, Command Line style: find "konsole" in your start menu or on the desktop if you have an icon there, and the command will be sudo emerge madwifi-ng madwifi-ng-tools
After either of the above 2 steps, you will need to have konsole open.. you will need to modprobe for madwifi or madwifi-ng he says.. your right command would probably be sudo modprobe madwifi-ng or sudo modprobe madwifi most likely the former. I haven't used modprobe in some time, so you -may not- need "sudo" on there, I'm not sure. but it should give an obvious sign if it's not correct when you try.
Hope that helps..