Catching Reshiram And Zekrom

I know most of you already did, but this for everyone else.  once you beat the Elite Four the first time, you go to N's Castle.  Once there, go to the top and you will battle it.  They are at Level 50.  Reshiram knows Dragonbreath, Slash, Extrasensory, and Fusion Flare.  Zekrom knows Dragonbreath, Slash, Zen Headbutt, and Fusion Bolt.  If you have no types of Pokeballs to catch them, or all of your boxes and party are full, then you can't catch it.  If not, you will repeatedly battle it until it is caught.  Then, you battle N, and Ghetsis.  I can't list all of their Pokemon here, so I'll give you this link: Justin Is Awesome.