Yup.
As a matter of fact you can. Heartgold and Soulsilver can interact with Diamond, Pearl, and Platinum the same way as they interact among themselves.
Use the wifi connectivity from your ds to your wii and you can battle with the Pokemon from Pokemon pearl, diamond, platinum, heartgold, and soulsilver versions
You trade Pokemon from Pokemon Heartgold and Soulsilver to Pokemon Diamond by going to the wifi room in the Pokemon center on the top floor. You also need to have a copy of Pokemon Diamond and have to have a friend or someone who has a copy of Pokemon Heartgold or Soulsilver. You will see someone there if you are going to trade with someone. Talk to the person you are going to trade with and ask them if they want to trade. The top floor is the Union Room no Friend Code needed the basement is the Wi-fi room, which requires a Friend codes
You have to be connected to wifi.
6.
You find were you can use it
if you are talking about your Nintendo wifi id you get it when you go on wifi
Technically,yes you can get Arceus in Pokemon Heartgold,but only by trading it to your Pokemon Heartgold game from Pokemon diamond,pearl or platinum.
Yes.
You can bring you ds with heartgold in it to a local gamestop, and receive it through wifi
Yes you can!
You can't get Darkrai in Pokemon Heartgold. You have to trade it from Diamond, Pearl, or Platinum.