Diamond, pearl, and other platinum versions
no you cannot't trade Pokemon from Pokemon black to Pokemon platinum or any past games.
trade from other games
You'll need to trade for it or migrate it from the older Pokemon GBA games. Trade
Yes, with Diamond/Pearl and Platinum.
you see all the Pokemon in platinum and trade from your other games like emerald, blue, fire red etc and that is how you find all Pokemon in platinum.
You can get a Chimchar if you trade it from games Diamond, Pearl, and Platinum.
The only way to get Lugia in Pokemon Platinum, is to use Action Replay, or to trade from other games.
as far as i know its not possible to obtain a "wild" groudon on Pokemon platinum. however you can trade it in from other games such as Pokemon soul silver.
no but you must take with you a ds Pokemon pearl or diamond. then when you get platinum you will have to trade it from the other games.
to get the old Pokemon into Platinum you trade them in from old games after you get the National Pokedex using the Dual Slot in the DS you put a gameboy game in and trade 6 Pokemon per game per day.
you cant you can get one by link cable(trade)from Pokemon d/p/pt(dimaomnd,pearl or platinum)you can trade from Pokemon diamond,pearl or platinum. soulsilver and heartgold are compatible with those games
No you cannot trade from Sapphire to Platinum. The closest thing that you can do to that is migrate from Sapphire to Platinum.