If you are seeing notifications for a Catalyst driver, chances are that is indeed still in your system. You may be able to remove it from Add / Remove programs (or programs and features under windows 7), looking for any AMD or ATI catalyst entries. If you don't know very much about driver removal I would suggest staying very far away from any driver sweeper or registry editing programs.
As far as your questions:
1.that score is right within the capabilities of that card. I wouldn't be at all suprised to see you could tune it and maybe make some other system modifications to get into the 3,500 range with that card, but I wouldn't expect more out of it than that. It's a solid upper mid range prior year model card. It uses a different rendering engine than the 200 series cards did, so its actually technically slower than a 260GTX unless the game takes advantage of the Fermi rendering engine, which the FFXIV demo might not. That also depends on the size of the monitor you are running too. That card isn't going drive a large monitor at high numbers. Anything over a 22" might give you some performance decrease with just the one card.
2. For your card, adding a second one would be known as SLI, or Scalable Link Interface. Crossfire is only for ATI cards. You can run two 460GTX's, or more, depending on the motherboard you have, but a 600 watt PSU isn't going to be anywhere close to enough wattage to safely run a second card. I'd need to know more details like what specific model motherboard you are running. Also, AMD / ATI motherboards tend to be optomized for AMD / ATI cards, not Nvidia cards. If you are going with an AMD motherboard, an ATI card in a crossfire array would have been a better route to go. I tend to prefer the Intel processors myself, and either way will work. You would see some added benifits from going ATI with that motherboard combination though. And yeah, see the above comment about staying far away from driver sweepers if at all possible.
3. Hard drive speed is definitly a possible problem, especially during character loading. There are slow hard drives out there, any of the western digital "green" series drives for example are decent at data storage, but horribly, horribly slow for actually trying to run anything off of. Knowing which hard drives you have would be helpful (speed and capacity, or model number is fine too). It could also be a drive with issues. Disk defragmentation is something that slows down loading of MMO characters on occasion, launching and running disk defragmenter may haelp (unless you already have a solid state drive, then disk defragmenting is useless) Upgrading to a faster hard drive will also help, though you picked a really really bad time for that as about 40% of the worlds hard drive manufactureing capacity is currently under water in Thailand flooding and won't be back online for another 5 months or so. Solid state drives are a huge speed improvement under windows 7, and definitly worth it, but they are spendy. A good sized one will run you more than your video card. Also, never, ever, ever buy an OCZ Solid state drive. Trust me on this. If a SSD is out of the budget, try looking for a 10,000 RPM Western Digital Raptor drive in a sufficiently large size. That should give you a 10-15 percent boost over what you have already. A SSD will give you about a 30% boost in loading speedup easily.
The last thing you will also want to check for Hard drives, is download and run the free "speedfan" utility and check the section for hard drive "S.M.A.R.T" errors. That section reports health of your hard drive. If either of the two main indicators in their are significantly lower than 90%, you have a hard drive that isn't happy and you need to replace it immidiatly. If they are up near 100%, your drive is probably fine.