If your on disk one
you gotta be really leveled up to do so. The best place to level up is the mideel area. You can get there on the tiny bronco. Just travel south and you'll see places you can park. Find the place with a green patch and run around on it. Only the green patch has head-hunters, they give you the most EXP and AP so far in the game. After your leveled up you gotta get gp....with no chocobo to race, no submeine** battles and no guy out front that will sell you em. Best thing to do is the bike game in the wonder square.Then when your ready with like maybe 100 - 200 gp go to the battle square and fight your heart out. you can talk to the guy in the white jacket not doing anything. He'll explain the rules. then when you have atleast one bp go and see the prize at the very bottom of the second page. There you go. you gotta get bp though

Disk 2 and 3
make sure you are well fit in a fight. then walk in and out of the front of the gold saucer not the ropeway, til you see a guy beyond the save point, he'll sell you a 100 gp's for 1000 gil. If you can't afford it try mastering an all materia and selling it before you try. another way is chocobo racing but that takes a while all by itself. Get enough gp and fight for bp. Go to the right or left of the guy in white and press ok to see the prizes you can win. If your good you can get the second to last prize. which is what your wanting