I spent about thirty minutes or so trying to find out how to do this. Getting Zorua isn't very difficult. I'm writing this up so people won't swamp the forums with "Where is the guy you tell the words to?" posts.
Once you get to Castelia City, you can get Zorua. Follow these steps:
1. Head down the road in between the Pokémon Center and the blue sign.
2. The building on your right is where Zorua is, we'll come back here later. Continue down the road.
3. Head past the fountain and down the next street.
4. Enter the first building on your left. You know you are in the right building if you see a Pikachu. Press the button on the elevator and go up.
5. When you head up, you should see a clown at the desk. You don't need to talk to him, I just felt like pointing it out. Talk to the scientist.
Enter the words in this order:
6. Once you have entered the words, you have access to the Transfer Machine.
7. On Diamond, Pearl, Platinum, HeartGold, or SoulSilver, place the Pokémon you want to transfer in your PC. You can only transfer the Crown Beasts and the Movie Celebi. They have to be those events and they have to be in your PC.
8. On your other DS, access download play, and on your other DS with Black and White in it, go down to the bottom of the menu, go through the prompts and your other DS will find the program to download.
9. After this... you can just kinda wait a little bit until the program stops sending the information.
10. When that's done, you can find the Pokémon in your PC.
Head back to the building with the blue screen on it with Celebi in the first slot of your party. Talk to the woman inside talking to the boy. Save before you talk to her if you want to soft reset for a particular nature. The boy is actually Zorua, she'll ask you if you'd like Zorua, and once you accept, you are given the choice of placing Zorua in any Pokéball you have in your bag. Then you may nickname it if you want.
Zoroark is much simpler.
1. After transferring your beast (or beasts, but you only need one), put it in your party and exit to Route 16 from Nimbassa City.
2. Head up to the fence area, go past the backpacker by the tall grass and head to the right.
3. Go past the tall grass. You know you're in the right area if you see a tree stump.
4. If you want to soft reset, save before you go past the cliff side.
5. Head up to the trailer and a woman will pop out. Surprise! It's Zoroark!
You do not have to have the beast you transfer in the first slot of your party. So you can have a Synchronizer if you want. You can also catch Zororak without breaking its Illusion. As soon as my battle started I threw a Quick Ball and it was caught.