The closest you get to a "default login" is the account named "root", which is similar to "Administrator" under WinNT/2K/XP.
This is printed out clearly during the installation when you're asked to specify your password.
So, just try "root" as the login, and whatever password you specified, however dont make it a habit to login as root, that's a bad habit, first thing you should do, if you didn't do it during the install, is to create a user for yourself, and use that one for everyday stuff, and when you need to do things like installing programs, use su and/or sudo.
Oh, and like BBWF said, pay attention, if you wanna learn(as opposed to just use) Linux, you'll have to pay attention as it won't hold your hand for you, and won't complain if you do something that might hose the entire system, it just sorta assumes you know what you're doing.