I'd like to recommend anki.
Anki - friendly, intelligent flashcards
It's a flash card program. It's free and it has a whole bunch of decks with Japanese vocabulary.
My personal opinion is you buy a kanji book like the one recommended ^, download a set of *vocabulary* flash cards, and start the program. I'd cut back to 10 new cards a day instead of the default 20, but I am a lazy, lazy man. When you see a new word, look up the component kanji in your book, read the nifty mnemonics, but then memorize the word, not the kanji.
(Heck, I'm so lazy I skip the "look up the kanji" part. There's more than a few words where I have no idea what the individual kanji "mean" but I know the word itself.)
It *is* possible to reach the point where, as long as it's in anki, you recognize the word instantly, but outside of that context you get lost. It's important to be reading Japanese as much as you can outside of anki to make your lessons stick.
Of course, when you only know 20 words or so, "live" Japanese is still impossible. You might want to consider rikaichan
rikaichan | polarcloud.com because you can hover over a word and it'll tell you what it is. The flaw there is it's a crutch, and it's easy to become addicted to it. You have to have the discipline to *try* to read a word first, before using rikaichan to look it up.
Now for something that I consider to be my personal secret. This is completely optional, if it looks like too much work just skip it. Rikaichan only works on digital data. I've tried many, many ways to look up kanji in pictures and books that I don't recognize. Multi-radical search is a pain. Hand written input requires you knowing stroke order, which isn't always obvious, especially when you're just starting. I have no idea why Japan doesn't have one, but China and Taiwan have DOZENS of shape based input methods. Cangjie has the best English tutorials, and it has the best kanji support as well.
Download it for windows here:
Pinyin Joe - Taiwan IME 2010 Update - New Phonetic, Changjie, Quick, Cantonese Jyutping Jyutpin - Office 2010
(You don't need office)
Learn about it here:
New Page 1
Practice here:
Cocoa Nuts
You might want to install this:
ChaJei (CangJie) Explorer
It took me about a week of serious effort before I was really comfortable with it, but I can look up kanji I don't know in seconds. Go to thunderbird, cangjie input, rikaichan: Got it. I'm faster than handwritten interfaces if the kanji has more than about 10 strokes. (OTOH, I'm in the uncomfortable position where I see 意 as 卜廿日心 first, and い second. But so far that's the only one to have gotten stuck that way. It was a hard kanji for me to learn for some reason. And it's a bit of a pain to be constantly switching between Cangjie input and Japanese input for okurigana, but IMO still better than your other options for kanji you don't know.)
So there you go, three suggestions, all of them flawed. Have fun.
Edit: D'oh, you posted while I was typing. Okay, you want to install rikaichan and the Japanese input method. When your textbook throws a new word at you, type it into Thunderbird or Firefox with Japanese input method on, hit space, it converts to kanji. Double check it with rikaichan to make sure you got the right homonym. You're on your own for memorizing. You could build your own anki deck if you wanted, with just the words from your book.