What can I do if I forgot my account name/email address?
Your account name is usually your email address. If you created the account from a PlayNC or NCSoft Master Account (usually only if you have multiple Guild Wars accounts) it will be username@plaync, or username@ncsoft, where username is a name you chose that you can look up in your plaync master account. If you are still stuck, contact support and see if they can help.
http://wiki.guildwars.com/wiki/User:Gaile_Gray/Support_FAQs/Contacting_Support
What can I do if I forgot my password?
Start the Guild Wars game client. There is a link below the password field that says "Reset password". You will be prompted for confirmation. After inputting that information, a new randomized password will be sent to your email account; however, this will only work if your game account is not linked to an NCsoft Master Account. If your game account is linked to an NCMA, you will not be able to reset your password, although you can change it by logging in and using the Edit Account option in the lower left of the Character Selection Screen. If you cannot recall your password in order to log into the game, or if you have other difficulties, contact support.
http://wiki.guildwars.com/wiki/User:Gaile_Gray/Support_FAQs/Contacting_Support