Without further ado, here's a, "Getting onto Arkaz for Dummies."
#1. Log into, "Multiplayer." You will be given a, "The Master Server is down," message.
#2. Log into any Arkaz server(Islands, Iron or Toloira).
#3. Select any character, then jump in game.
#4. Upon logging in, you will be unable to do anything. You will be booted after approximately 1 minute unless you complete the following steps #5 and #6.
#5. If this is your first time signing in, you will be asked to set your password. The command is
!pwset [yourpasswordherewithoutthebrackets] [yourpasswordherewithoutthebrackets].
Note: You do, as noted above, have to type the password twice for confirmation; the command also begins with a ! - don't forget that.
#6. You will be asked to authenticate. The command is !pw [yourpasswordherewithoutthebrackets].
Note#1: You will only have to perform #5 once. In the future, you will only have to perform step #6 upon logging in.
Note#2: If you leave the server for more than 15 minutes and then log back in, you will be prompted to re-authenticate.
Some things to remember...
First and foremost, don't reuse your password from the forums, from your email, from your actual Gamespy account or from anything else that you wouldn't want compromised!
If something seems amiss, come talk to us! Send a private message to the team on the forums, or get in touch with someone on IRC. We'd rather hear about it than find out about it!

If you're having trouble, both the server-message window and your character journal have instructions!
If you need to reset your password for whatever reason, just repeat step #5!
If you forgot your password post in the Ask The Team forum for DM help.