Macs aren't very good computers for the price you pay for them. Even running Windows, you might get comparable performance to a computer you would get for about half the price.
FFXIV requires a very beefy CPU as well as GPU. Even just installing Windows 7 on a 35GB partition isn't going to cut it. Windows 7 needs about 20GB's free for just the bare bones. I'm sure FFXIV will eventually need more than 15 GB's, even if it doesn't, you're going to want the OS to breathe a little.
You can build a very capable rig for FFXIV for around $1,000 (More or less depending on what you expect to gain out of it). If you MUST have it on a Laptop, and money is no object, consider a model by Alienware. If you care about how much you're actually paying and want a decent laptop, go on Newegg and check out some Toshibas. Make sure you're running a decent multi-core CPU, good RAM (At this point, don't bother with DDR2, go for DDR3) and a very recent GPU, something equivalent to the 200 or 400 GTX series.
There are many ways to get Windows. I get my own free copy from school because I happen to be an IT student. You can buy directly from Microsoft if you wish. You're going to need Win7 Home Premium or Ultimate if you'd like all of the extra features. That'll run you around $200 to $300 (Estimation, I haven't actually checked in a while). Or you can pirate, and get it free, not that I'm condoning that, but it *IS* an option.
I don't think FFXIV will run natively on Mac OSX, but there is always the option of installing it on a Virtual Machine via VMWare or Virtual Box, but that might be over your head and really won't be a good idea unless you have a killer machine, which most Macs aren't (Sorry, just being honest).
My advice, sell the Mac, put the money towards a really good PC or Laptop, and if you need/want Mac OSX that badly, run it virtually on your shiny new PC. Along with Ubuntu Linux and any other OS you might like. I like OpenSolaris myself, but Win7 is my main one because I'm a gamer.
TL;DR Ditch the Mac, get a PC with a Dual/Quad core CPU with lots of Cache and ~3.0GHz. 4+GB DDR3 RAM. Geforce GTX 260 or better. 1+TB Hard Drive. Fans. Good to go.
*RETIRED* KMFDMKid is now Zanza's mule...RDM 75/WAR 75/PLD 75/DRK 75/WHM 38/NIN 37/THF 37/MNK 25/BLM 40/SAM 37 Gear: Solo
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