One good way to improve your Japanese is by using the Nintendo DS as a learning tool. Here is the one that I've gotten the most benefit from, Kanken DS 3 Deluxe. The game takes you through the different levels of the Japanese Kanji Aptitude Test or Kanken. This takes you through the same path of Kanji learning that an average student in Japan would go through, starting at level 10 (1st grade) and moving all the way up to level 1, which even most Japanese people aren't able pass. I've probably put around 70 hours into the game since I started about 1 month ago and just recently finished level 7 (4th grade). This game has really kept me motivated because I can always see how much I've progressed from when I first started. It always feels good to go from miserably failing at the beginning of a new level to getting a near perfect score after enough reviewing.
The main feature you will want to use is the challenge, which gives you a 45 or 60 minute time limit to take a quiz exactly like you would see on the actual test. Early in the game you will just be either writing the hiragana for certain words, or be given hiragana and have to write the kanji that would fit in the context. The game has a great Kanji recognition system and you can view the proper stroke order if you miss a question. You can also mark any questions you are unsure of and add them to your My Kanken checklist, and review it later.
The game is completely in Japanese but most of the menu's and test questions are self explanatory, and here is a walkthrough explaining them and how the game works. The first few levels are fairly easy and cover basic kanji, stroke numbers, and some hiragana and katakana, but once you reach around level 7 the difficulty increases and you will learn more things like antonyms, onyomi and kunyomi, and you really have to go back and review the words you don't know. I wouldn't recommend the game for a complete beginner to Japanese, you should at least have a basic understanding of some of the language and maybe go through Heisig's or kanjidicks method of learning the Kanji first (check out Chi-chan's blog for some good tips on this).