I've used the Dream World once. You access it through the Pokemon Global Link website. You make an account with Pokemon.com, and link that to the Global Link Site. Then you register your copy of the game with the GL site. The website will tell you how to do this. The GL site will keep track of how many online battles you've won/lost, who you've traded with, who your friends are, etc. To use the Dream World, access the C-Gear, and select Game Sync under "Online." You'll be taken to your Pokemon boxes, where you will choose one of your Pokemon to "tuck in." After about two minutes that Pokemon will show up on the Dream World portion of the GL site. Once you enter the Dream World, you can grow berries (something you can't do in the main game) and trade berries and items with your friends. (People on your friend list can access your area of the Dream World and pick up items you leave on a shelf.) Most importantly, the Dream World is the only way to obtain many of the Pokemon from previous generations. You wander around areas of the Dream world and meet Pokemon. If you win a Mini-game with the Pokemon you met, they are befriended. When you reach the Dream Tree (I'm not even gonna try to explain that) you can choose one Pokemon you befriended along the way to send back to your game. (I got a Mareep!) Once you've woken up your Pokemon on the site and the DS, you enter the Entra-link on the game, and you can capture the pokemon you sent over from the website. You are given a special Dream Ball that automatically succeeds in the capture. Whew. Does that make sense? Pokemon you get through the dream world usually have different abilities than their in-game counter-parts. For instance, Dream World Ditto will transform immediately on entering battle, so you don't have to waste a turn. You can find a complete list of all the Dream World Pokemon currently available, as well as everything about every Pokemon game ever, on Serebii.net.