[MMM]

That's great advice, Masaegu.

In general, you should start learning hiragana on your first day of Japanese study. You should couple this with basic phrases. Hiragana and Katakana shouldn't take too terribly long to learn. I used to teach high school Japanese, and taught about 10 characters a week, so it took about 3 months, maybe a little longer, to learn both. A motivated person could do it much faster, though. Basically getting hiragana down is the most important first step. Then you can write any word. (You might notice most children's books are written entirely in hiragana.) At the same time, learn some vocab, and play with it. How they flow together will give you exponentially larger abilities to communicate.

If you know 10 verbs, and 3 conjugations, then there is 30 ideas you can put together. Learn just three more verbs, and that number jumps to almost 40. Learning JUST vocab isn't enought...and really isn't even that useful, as Masaegu said. The vocab will come, it's learning the WHY sentences are structured the way they are (particles and conjugation) that give you the ability to communicate and create your own sentences.