There's an AQW tutorial section so you might want to check that out
Username grabbers - released my source yesterday: http://www.mpgh.net/forum/showthread...816&p=10218971
But there's no defined way of making one (all games are different). AQWorlds is also a flash game.
Crackers - it's just bruteforcing. Find the login link used by the game and use http requests to check different usernames and passwords.
If you're looking at specific game, email me and I'll try help you out email@example.com