Your only hope with getting the login information for that account would be to contact Guild Wars Support and take it up with them - they are the only ones who will be able to verify that it's your accoutn and provide you with the login details.
www.guildwars.com/support/
What you'll need is : any receipts you might have proving you bought the games, any cd-key cars/papers from the games as well as any ID papers you might have (ie driver's license, birth certificate, citizenship certificate, etc).
If you don't have the receipts/cd-key's.. not sure if they'll provide any details, but I'd say it's well worth a shot.. just put a support ticket in.
If you d remember your username & password, all you need to do is install the game and your good to go.. but if you don't know them, you will need to contact support.