I've been intensively learning for the past 4.5 months (that's not the first time I tried, but now I'm serious about it), but that's unrelated to FFXIV. Before that time I had previously gone through Genki 1, so that'd be a good introduction, but it's only going to teach you very basic, textbook japanese, so move on as soon as you can.
Personally the first thing I did after that was learn the Jouyou Kanji (the 2000~ roughly most common characters) like I would an alphabet, which took me 50 days using Anki (flashcard program, google it) and no real special technique, just regular memorisation. Though some people seem to think this is unrealistic... I guess it depends on your memory.
For grammar, read through up to and including special expressions or so http://www.guidetojapanese.org/learn/grammar.
After that I've been studying grammar according to the JLPT syllabus.
Then for grammar I use these lists of sentences, importing them into Anki http://smart.fm/series/3318 http://smart.fm/series/3321
which'll have taken me around 4 months by the time I finish. They have audio which is handy. After these one'd be reasonably equipped to learn from native sources, probably. Until then, use whatever you want for listening practice... I guess Rosetta Stone can give you some of this stuff but I don't know what it could provide that would make it worth so much when you can find similar stuff for free.
Finding a friend to chat with online or talk to IRL in the language helps too. (I'm so grateful to my penfriend for providing me free accomodation for when I visit ;D)
My reasons are that I need to get to a high level to do graduate study in Japan, so I'm being expeditious about the process... but I'm assuming you're wanting to be too.
Let's just hope JP input is possible in the US version of FFXIV is possible. >.< Edited, Dec 21st 2009 11:50pm by Dizmo Edited, Dec 21st 2009 11:51pm by Dizmo