In some pokemon data, I have noticed that you said it would appear in a route or something close to that in the pokemon locations. What do you mean by that? (sorry for a dumb question, but I am new to Diamond and Pearl)

You know how the DS has two slots : one for DS games, one for GBA games. Well, when you insert another GBA game, such as PokemonEmerald, that unlocks pokemon in Pokemon Diamond/Pearl. When you insert LeafGreen, an example, it unlocks Magby at the summit of Stark Mountain. See?

so you just put it in the DS and it will pust pop up? or do you have to walk around?

wow, i just did it and after awhile of walking i found what i needed!

Mod Edit: Do not double post. I've merged your posts together.
-JsX™

When you insert the ds, you start your d/p game normally. on the start screen where you select the game to play, modify your Wi-Fi settings, or start a new game, a new option will appear. It will say "Migrate from {game name}" Select that option and click yes, meaning you understand that you will not be able to trade the pokemon back. After that, you select 6 pokemon to bring to your d/p game. It cannot know hm moves, such as cut, surf, rock smash, etc. You can only do 6 per day and you have to have 6 in there. you can't do less than six. After you select the six you want to bring over, it will ask you again. click yes. then it will save and then it will bring you back to the title screen of the D/P. Select your game. Then go to pal park. Talk to the guy at the counter and he will talk to you, then give you six park balls. They never fail. Next, you go in and find the pokemon you sent over in the different sections : Plains, Forest, Lake/Pond, Mountain, and Sea/Ocean. You can find where to find your pokemon here. At the bottom of the page, just select the region you're looking in and see if its there. Just keep looking. When you are finished catching all of them, you will be escorted out and given a prize, such as a berry. Hope I helped.

Thanks a lot. This helped a lot. So now what would be the case if I saw insertion and it refers to a route number?

That would just mean with the certain game inserted, you would now have a chance at finding that pokemon on that route.

In fact, that guide just got posted this evening! :O

I've inserted my FireRed Cartridge, and I've been hunting for both Growlithe and Elekid for such a long time it's getting frustrating. Now, I haven't completed the Sinnoh Dex/gotten the National Dex, would that be why I'm not finding any of these?

Yes, it would. I'm going to lock this thread because 1) it was in the wrong section in the beginning and 2) we already have a help thread in the Sinnoh forum. If you need any more help, please post there.