Odaiba is a little confusing - actually the train line you need is the Rinkai Line (a subway line). If you look at the Yamanote line - the circle line around the center of Tokyo, on the bottom end is a station called Osaki. You can catch the Rinkai line there. The station you need is actually called Tokyo Teleport (great name hey) - and it's about a 5/10 minute walk to Decks depending how fast you walk - it is signposted so don't worry.
The other way to get to Odaiba is by taking the Yurikamome line - see this link for details - scroll down and you'll see the map
Tokyo Travel: Odaiba (Daiba)
Odaiba is actually built on a man-made island near Rainbow Bridge.
Yes you are right - Tokyo Game Show is near Disneyland so maybe you can combine the 2 if you want to
