Before I consider this...

[Ouch!]

Since the game came out in 2002, unless your laptop is older than that, you can probably run the game well enough. A lot of people these days hack the registries and use other third-party programs to make the game look prettier, but the base specs are relatively low. I don't know them off the top of my head anymore.

Like Levian said, purchase the 2008 Collection. It has all the expansion packs, most of which are necessary at some point or another. It's also very cheap, so no need to worry about spending more than you'd expect for any other MMO. I'm pretty sure that bundle is the only version on the market right now anyway. They just announced the Ultimate Edition today. It contains all four major expansion packs and also the three mini-expansion packs for $19.99.

Square Enix has said they'll continue supporting FFXI as long as they have a sufficient number of people willing to play. I imagine that means, like Levian suggested, they'll keep running even after FFXIV is released. They've referred to the possibility of merging servers as it becomes necessary, but we'll just have to wait and see how that goes.