Before I came to Japan, I learned a decent amount about the Japanese language and the Japanese culture, all for free and from the Internet. Here are the top ten websites that helped me and maybe they'll help you too.
1. JapanesePod101.com: This is free daily podcast based out of Tokyo. Every day there is a new conversation about 10 minutes long with followup grammar and cultural explanations. You can find the podcast in the iTunes music store.
2. D-Addicts.com: This is a torrent site for sub-titled Japanese dramas. For me, it was essential for learning how Japanese was spoken. I highly recommend downloading My Boss, My Hero, Liar Game, and my all time favorite Stand Up! You'll first need a torrent client such as uTorrent or Azureus.
3. 1, 000 Kanji Page: If you want to learn kanji, this is a great place to start. You'll first need to learn the Hiragana alphabet and then mentally convert the website's romajii into Hiragana. There is no other way to learn kanji than to just grab a notebook and put some serious time in. Good luck.
4. JR Train Site: Once you get to you Japan, you'll need to figure out how to get around and this site is great for it. You type in where you're coming from and you're destination and it tells you where to change lines. I usually start out most long trips by visiting this site.
5. Japan Talk: This is a great podcast for keeping up with the news from Japan in an entertaining format. New episodes are posted every week and aside from the website, you can find Japan Talk in the iTunes music store.
6. Skype and Xlingo: One of the problems I encountered in learning Japanese in America is that there was no one to speak Japanese to. With Skype and the language exchange site Xlingo, you can find people in Japan to talk to. Although it's difficult to meet people at first, I had a great experience with this and one person in Kobe even sent me a care package when I got to Japan.
7. Rikai-Chan: This is a Firefox add-on that translates individual words in Japanese as you surf the web. You may also need the accompanying dictionary as well.
8. Forums: To get a first hand account as to what other foreigners think about Japan, you might want to drop by some forums such as GaijinPot.com and FuckedGaijin.com. Also sometimes crude and off-topic, they could be a good source for gaining some inside knowledge.
9. Stars21 Translator: In case the Rikai-Chan kanji translator doesn't cut it for you, I found this site to be the most accurate Japanese to English translator. I actually prefer it to BabelFish. For some reason, the site shrinks my browser but whatever.
10. The Japanese Page: Honestly, I haven't spent too much time on this page, but Rivers Cuomo is a sponsor so it must be half-way decent. There seems to be a lot of grammar stuff on there. It might be worth a look.