1.) a quad core processor is pretty much an absolute necessity for this game.
2.) Anything under a 5600 or a GTX 4XX should really be replaced.
3.) 4G of RAM? Slightly on the low side there, I'd recommend at least 6G and if you plan on running anything else but 14 while the game is running, at least 8G.
Also, if this system is a laptop I highly advise against trying to run XIV on any laptop. Get a mid-range desktop or (if for some reason you absolutely MUST use a laptop) be prepared to shell out a ton of money for a laptop powerful enough to handle 14.
Either way this computer is not really worth upgrading as you'd have to replace pretty much everything.
I'm sorry, I know that a lot of people have pretty much decided that Quad-Core is a requirement, but it really isn't. I have a AMD X2 2.8 Brisbane w/ 4GB Mem (Win XP) and an ATI 5770 and I score around 3100 on low, and around 2500 on high...both cases reflect a FPS above 30 (constant) and a CPU load no greater than 70%.
I scored a 1980 on low settings (can't do high, because my monitor is only 1440 x 900) The benchmark runs, but i can't see the score.
what do I need to upgrade?
AMD X2 Athlon 6000+ 3GHZ dual core
ATI radeon 3850 512mb
4 gigs of ram
At bare minimum, you're going to have to upgrade your video card. If you're running Windows XP, more memory isn't going to do anything for you. Check your power supply, and make sure you have a 6-pin connector and are at or above 500 watts. Shoot for an ATI 5750 to 5850 video card (currently, 5770's run around $150...good midrange card and price) or an Nvidia GTX 460 (equivalent midrange card around $200-$250). Ensure you're motherboard is PCIx 2.0 compatible as well.
If you have an AM2+ socket motherboard, you can option upgrading to a Phenom X4 if you want to go Quad-Core. Newegg has OEM Phenom X4 CPU's for around $80, which is a great deal. Good luck :)