Getting Eevee to evolve is pretty simple
Firestone=Flareon
Waterstone=Vaporeon
Moonstone=Umbreon (Not possible. It evolves when it likes you at Night
Sewstone-Espeon (Not possible. Stone doesn't excist. Evolves when it likes you at Day
Icestone=Glaceon ( Not possible. Stone not excist.Evolves when likes you and give it Rare Candy near Snowpoint City.The Icey Rock
Leafstone=Leafeon (That might be 1 WAY! but going to Etrena Forest stand at the grassy mossy green rock and give it Rare Candy
Last but night least
Thunderstone=Jolteon
This was made by-Joshua,a Pokemon HeartGold Trainer
It Doesnt need to have a good level
after getting your national dex do to bebe in hearthome city and she will give you a Pokemon called eevee level 55
if you have an eevee you go to the path before snowpoint city you find the snowy rock and level up your eevee near the rock
level up eevee near it and it evolves into leafeon.
I'm not sure if you can catch Eevee in Pokemon pearl but you get it as a gift from Bebe in Hearthrome City after you get the national dex.
level it up during the night time with high friend ship
level up an eevee in Eterna forest by the mossy rock by the first entrance to the forest.
you have to level it up in the day until it loves you. for umbreon you have to level up at night until it loves you
In Pokemon Diamond and Pearl you can receive Eevee from Bebe in Hearthome city.
You need to get an Eevee first and then use a Sun Shard or level it up during the day.
Gain max friendship, and raise eevee one level at night.
EEVEE GROWLITHE and VULPIX