Supposedly I'm at disc 4 and I have saved on some island and I have the flying ship thing. I also can't remember if I defeated Ozma. How can I find out where I'm at now? It's been years since I've played this game...

Disk 4 is right at the end, so you're right at the end...
I guess you have Memoria or any sidequests you've not yet done. Or possibly a visit to the Black mage village. Thats about all you do on disk 4.

I think I completed the Chocobo sidequest, as I have Zidane's ultimate weapon. What about Ozma? How do I know if I've beaten him?

I think I completed the Chocobo sidequest, as I have Zidane's ultimate weapon. What about Ozma? How do I know if I've beaten him?

Just check chocobo's air garden. fly over the dark shadow that can be found around the map and use a dead pepper to fly straight up to it. If you visited the air garden before you can find where the shadow is on the map.

Ozma is there if you want to check

Alright. I'll try that. Thank you for your reply, Moogle.

If you defeated Ozma, look under Key Items for something called "Strategy Guide"...

Aw, I can't check it anymore, as my bro both a PS3. We've been playing CoD only. Oh well, thanks for the replies, guys.

as my bro both a PS3.

Babelfish does not help with this!

He meant Boat obviously

Yes, I meant boat. Thank you, Andy.