Don't know much about FAQs (try Gamespot or GameFAQs or just google Omega Weapon FFX), but Omega isn't that hard. If you have CW for 3 characters, and your stats are around 100 for Strength, Defense, and Agility, he should go down after a long, but not particularly straining battle. If your characters are really weak, you can use Aeons to block his attacks (plus get an Overdrive attack in).
Originally Posted by FFX Official Strategy Guide
Although Omega Weapon's HP figure is extremely impressive, his fighting skills are not much to write home about.