There is no such thing as an ender cat on minecraft. If you are talking about an ender mite, then they sometimes have a chance to spawn when you use an ender pearl to teleport.
There's no spawn egg for enderdragon.
Ender Crystals could be spawned using Spawn Eggs with ID 200
There are no seeds to spawn in the ender realm but there are definatly a few where you spawn near a stronghold but they arent easy to find on the internet because of the 1.2.3 seed change and its is unlikely you will find one by luck.
you cant yet the egg is just for decoration right now
spawn it with an ocelot egg
They just naturally spawn in jungles. Unless you're in creative, where you can use an ocelot spawn egg to spawn one in.
Technically, there is no real "end" to Minecraft, but you could count the defeat of the Ender Dragon as the furthest point in the game.
You can't unless you're using some sort of world-editing program. There is only one ender dragon per world, and it is in The End.
You can't respawn the Ender Dragon in Minecraft without some kind of mod. Single Player Commands and the Essentials Bukkit server plugin can both be used to spawn mobs.Whatever you do, don't spawn it outside of the End, unless you don't mind your world being bombed.
do /summon EnderDragon
The Ender Dragon is a part of Minecraft, not a mod. You probably need to update Minecraft.