>Once you beat the elite four and go to Kanto, in Fucia City where the Safari game used to be, there is the Pal Park. Once you get there, you can migrate your pokemon if you have both games in your DS.-Information
You will first need a DS with a game-boy slot. Either a normal DS or a DS lite. Then when you have Soulsilver and Firered in the DS go to Fushia City and enter the Pal Park.When you talk to the man at the counter this should start up a process of migrating your Pokemon from Firered to Soulsilver. Repeat this process until you get all your desired Pokemon. If this doesnt work for you there is something messed up with one of your games.