Once you beat the Elite 4, go talk to Celio. He will tell you about the Ruby. Go up to Mt.
Ember. Then travel right, and then up. If you ever saw any Team Rocket members there, they
will be gone. Enter the door where they once stood, and make your way through the maze.
There will be a few Jhoto pokemon there. Finally, when you get to the Ruby, grab it. bring
it to Celio. He will tell you about the Sapphire and give you the Rainbow Pass, which
enables you to go to the Sevii Islands. Go to Island 6. Get a pokemon out of your PC that
knows Cut. Keep going down untill you find the Dotted Hole. Face directly at the door and
use Cut. The pattern for the holes is Up, right, down, then left. Grab the sapphire. A
scientist will come down and ask you for the sapphire. You will have to give it up. Find
the Rocket Warehouse passwords from [somewhere. I don't know]. Then go to Rocket Warehouse
on Island 5. Find your way around it then battle the scientist. If you win, he will give
you the Sapphire. Give it to Celio and he will enable the Network Machine. 
I hope this helps for those of you who need to trade with Ruby and Sapphire versions!