How do you get the 3 legendary dogs in Pokemon FireRed?

To get a legendary dog, you must first obtain the National Dex. Once you ave it, the dog that appears is determined by your starter. If you chose Charmander (fire), a Suicune will appear. If you chose Squirtle (water) a Raicou (sorry about spelling) will appear. If you chose Bulbasaur (grass) an Entei will appear. The dog will be roaming around the game in random fields. Once you see it, it's current area will be shown in the pokédex. Do not use fly to try and get it, as the legendary dog moves as far as possible from you when you use fly.