"you can't"
Actually it is possible, not to trade directly from G/S/C to D/P
But to get the Pokemon from the G/S/C series to D/P
Long winded but all you need to do is trade Pokemon from G/S/C or even R/B/Y
trade those to either R/S/E or Fr/Lg and from there trade them to D/P
P.S. R/B/Y = Red, Blue, Yellow
G/S/C = Gold, Silver, Crystal
R/S/E = Ruby, Saphire, Emerald
Fr/Lg - Fire Red, Leaf Green
Another note is that people on eBay actually sell Pokemon on eBay if you cant catch certains one's, I'm not advertising as I'm not selling them and don't condone it
Hope I help anyone with this particular problem
EDIT
actually I've been informed it's even more complex, but still possible
As I've been informed you cant trade G/S/C or R/B/Y Pokemon directly to a GBA game such as fire red
Here is the only way to do it:
1. Trade Pokemon from R/B/Y or G/S/C to Pokemon colleseum on Gamecube
2. Trade those Pokemon from Collesseum to R/S/E or Fr/Lg
3. Insert the GBA game into the DS and trade to Pearl/Diamond
Sorry for the earlier mistake
Yes, just trade it from Pokemon Diamond or Pokemon Pearl.
yes you can but you cant trade from pearl , diamond , platinum , soul silver , heart gold to Pokemon black & white
unfortunately you dont you have to trade it from diamond or pearl
To get both leafeon and glaceon in Pokemon soul silver or heart gold you have to trade it from diamond pearl or platinum.
You'll need to trade it from Pokemon Diamond, Pearl, or Platinum.
trade it from Pokemon soul silver
Trade it from Crystal gold or silver
yes you can
Yes by finding someone who has pearl and then trade with them.
Yes, just trade it from Pokemon Diamond or Pokemon Pearl.
yes you can but you cant trade from pearl , diamond , platinum , soul silver , heart gold to Pokemon black & white
I'm not sure if you can but the way i know it is to trade from Pokemon diamond, Pokemon pearl, or Pokemon platinum. You will have to trade it.
Yes, much like it's predecesores (Ex. Pokemon Gold and Silver could trade to Crystal) Pokemon Platinum will be able to trade Pokemon from Pearl and Diamond.
You can't get him.you have to catch him from palpark or trade from Pokemon soul silver
you dont. you trade it from platinum , diamond or pearl
unfortunately you dont you have to trade it from diamond or pearl
no you can not...but you can trade heart gold and soul silver Pokemon to diamond pearl and platinum