I don't think there is anyway to download an older version. I bet the website you are following was made when xcode 3.1.4 was the newest version. You could try searching for torrents of the version of xcode you want, but the might be dead since the version you want is older.
Why do you need 3.1.4, instead of 3.2.6? Does 3.2.6 not work with Leopard?
You can go here to download 3.2.6, I think you need a free account.
