It also depends on the server. I would advise going on the canned chat servers, there isn't really a decent account to crack on those servers. But it's best to start there. You also forgot battleontown, ballyhoo, and any other somewhat crowded maps of the game.
There is a folder in the .rar named ACCOUNT CRACKER click on it.
Underneath the fscommand there should be a .exe program called Armjldian account cracker. This is what you need to use to hack accounts. Look for my tutorial on how to use it.
Now as for the "How to grab usernames question".
You need to open the Username Grabber.exe in the .rar folder.
Then log in and press the right arrow. A window will open and you can pick up automatically ( Which I recommend to go on battleon-Cysero) the maps that you wanna catch the usernames or you can pick up the names manually by changing map by yourself and manually pick-up usernames.