I usually skip the chocobo thing. You don't need the chocobo to avoid the Midgar Zolom, but it's hard. If you don't have a lot of money, I suggest you do things that way. Save your game at the edge of the swamp, wait for the MZ to move to one side, then run as fast as you can close to the moutains until you reach the Mythril Mine entrance. Save. Don't put Aeris in your party. Play up to the Turks. When that's done, reset. Put Aeris in your party and watch the Turks scene again.