First learn Japanese's alphabet, kana (hiragana and katakana). They should only take a week to learn. Practice reading articles until you can read them quickly.

Next learn kanji. The government has a list of characters you need to know for everyday use. You can find it here: http://en.wikipedia.org/wiki/List_of_j%C5%8Dy%C5%8D_kanji. Make sure you organize the table by grade level, starting with grade 1. I went by grade, first learning the English meaning and on'yomi (how the character is pronounced when with other characters), then going back and learning the kun'yomi (how they're pronounced alone). When you finish grade 6 you will be amazed how much you can read.

After that you can start reading simple stuff on the internet. There's a good Firefox plugin called Rikaichan which will let you mouse over a kanji to get its meaning and pronunciation: http://www.polarcloud.com/rikaichan/

When you've finished the secondary school kanji ("S" on the chart) you can start reading offline stuff in books. I recommend you buy a Canon Wordtank so you can quickly look up new words. Read something fun like a translation of your favorite author. Good luck!