you have to follow raikou and entei around on the map. you have one attack then thay flee. you decrease there health then capture them with your pokeball of choice
I don't think you can refight any legendary Pokemon except the wandering dogs.
It will be very unlikely.
If by enti you mean Entei the legendary dog then yes, all three dogs are there.
You need to migrate each from either firered or leafgreen or you can trade with heartgold and soulsilver after they got them.
Yes, the legendary dogs Suicune, Entei, and Raikou will be able to be caught in Heart Gold and Soul Silver.but don't forget the legendary Pokemon ho-oh and lugia
Entei is a roaming legendary, to find it you have to go to Burnt Tower, and go to the basement. Once the legendary dogs have run away, you will be able to track Entei on your Pokegear.
there are many legendary Pokemon in Pokemon heartgold, but the best is HO-OH
I put a link to a guide all about legendary pokemon in HeartGold in the related links.
right now (december 22) there is an event at gamestop where you can get one of the legendary 3 dogs shiny
The only way to get the Legendary Beasts in Pokemon Pearl is to find them in FireRed, LeafGreen, HeartGold or SoulSilver, catch them and then migrate them over to Diamond via Pal Park.
No legendary can lay an egg except for manaphy which gives an egg to phione and you can not get manaphy or phione in heartgold
In HeartGold you can catch Kyogre.