Cross Stinger

Remove the Rockets from Island 4 and go to the Dotted Hole in Six Island's Ruin Valley. Go inside and fall through the hole, then on the floor below fall through the hole to the north, then the one to the west, then the east, then the south. At the bottom is the Sapphire, but a Scientist will snatch it and flee to the Rocket Warehouse on Five Island, to which he'll give you the second password and hide until you remove the Rockets from there and defeat him.

acgmindmaster12

If you have the Rainbow Pass go to 10.

Getting the Rainbow Pass:
1.Beat all of the gym leaders up to Blaine and beat him.
2.Go to meet Bill to get the Tri-Pass.
3.Go to Two Island and talk to the man in the Game Corner.
4.Go to Three Island and beat all of the Bikers.
5.Go to Berry Forest and save the little girl.
6.Go to Two Island and talk to the man and return to Bill.
7.Return to Cinnabar Island.
8.Beat Giovanni and beat the Elite Four.
9.Talk to Bill and get the Rainbow Pass after getting the Ruby.

Getting the Sapphire:
10.Go to the Dotted Hole.
11.Get to the bottom and get the Sapphire.
12.Go to Rockets Hideout and get one of the passwords from a Rocket.
13.Go to Mt. Ember and defeat the Rockets that are close to the peak of the mtn.
14.Go to the Rockets Hideout and use both passwords to get in.
15.Beat the Scientist that has the Sapphire. He would be hard if you didnt already beat the Elite Four so bring strong pokemon.
16.Make sure you get the Up-Grade because it's the only thing to evolve Porygon.