Matters not whether you have Garage Band installed or not. Forgotten password needs a solution, if not today then some day soon so let's just do it.
You were on the right track to boot to the install DVD (not sure why you call it CD) to reset your password or, for that matter, the root password. Are you sure you enabled root user? It is not an active system user when you first turn on a new MacBook. You would have had to go through some deliberate steps to activate it. Normally only very advanced Mac users, like me :) go to this trouble. There is nothing about enabling root user that will affect your chances of resetting your normal admin password.
You don't mention why booting to the DVD failed. It should succeed unless your install disc is damaged or it is not the one that came with your MacBook. I will continue on the assumption you cannot use your DVD to reset the password.
To reset the root user password, restart and hold ⌘ and S That starts the Mac in "Single-user mode". You'll know you are seeing single-user mode because the screen will fill up with white geeky text on a black background. Release the two keys when you see this. Wait until the last line says "sh-2.05a#" or "Localhost%#" and then follow the steps below. Don't type the " marks and be careful to type any spaces.
Type: "/sbin/mount -uw /"
(You will then see various services starting up.)
When the Localhost%# prompt reappears,
Type: "passwd root"
Type whatever you choose for a new root password.
OK, if you didn't really activate root user, but you just want to reset your admin user password (and still can't boot to the DVD), restart and hold two keys together: Command key (⌘) and the "S" key. Wait until the last line says "sh-2.05a#" or something similar. Then go ahead with the steps below. Don't type the " marks and be careful to type any spaces.
Type "/sbin/mount -uw /"
Press Return. (Nothing appears to happens, no problem. Also, you will see # again. That's fine; ignore it.)
Type "rm /var/db/.applesetupdone" (The normal format of Mac OS doesn't care about upper case.)
Press Return. (Now stuff appears to happen.)
You will finally get past the "Welcome" in a dozen languages and then you can create a new admin user. It should be a different short name from your old user.