You can send them from heartgold to black(you cant send them back though)
Note: you will need 2 ds.
You can do this by going to the tranfer lab.. You get to it by going to black city and go
left to leave the city then youll find the lab...
When your in the lab you will need to talk to the guy. He will tell you to turn on the
other ds(with heartgold) and put download play.
After you do you can choose which pokemon to transfer(cant have hm or items)
Then youll have to catch them by shooting a pokeball with a bow.

Poke transfer lab on route 15. You need two ds's with heartgold in it and go on downnload
play. Then you can transfer them.