I've compiled a few helpful links for writing in Japanese, learning the language, online dictionaries, kanji/romaji converters, etc. (っ´∀`)っ I hope these help you!
Basic Japanese Lessons: Just as the title says, this site has good basic Japanese lessons. Start here if you're new to the language!
Japanese - English & English - Japanese dictonary: To use this dictionary, just look at the middle of the page. If you're looking up a word that's English and you want it's Japanese translations, then be sure to have the drop-down menu set on Japanese, and vise versa.
Romaji Converter - Katakana version: The only thing you have to change is "neko" to the romaji you want. Copy and paste the hirigana you're given, and there you go! Use it in the forums if you'd like. You can use this to turn romaji (english text) into Japanese katakana. This does have hirigana as well, but the one below has more correct hirigana.
Romaji Converter - Hiragana version: The only thing you have to change is "neko" to the romaji you want. Copy and paste the hirigana you're given, and there you go! Try using it in the forums if you'd like.
Romaji Converter - Kanji version: This one's a little different than the websites above. You can use this to type romaji (such as "Neko"), and it will give you the kanji/readings for neko, or you can type "cat" and it will give you the kanji and readings for cat. Just make sure to press the right button when submitting. (Example: If you type "cat", press EN -> JA, and if you type "neko", press JA -> EN)
Kanji Translator: This one can be quite useful. Use this to translate kanji that you don't know, or if you don't know how to say it. For example, paste 猫 into the box, and select "detailed word info" as the option. It will tell you the meaning of the kanji, it's readings, etc.! You can try out the other options if you want to, as well.
Your Name in Japanese: This one is quite well known here, but I'll still list it...get your name in Japanese!
I will add more links if I kind some good ones. Enjoy!