You want an encoder or a decoder? If you just want all the characters to show, chances are that your browser is just configured in the wrong way. In IE, just go to View >> Encoding. Then, choose "Japanese" (if there's more than one option, try all of them). This would solve the problem.
If you don't have a ASCII Japanese font, as soon you click on the Japanese, IE will request to download it. Just accept. On Firefox, Anastar explained pretty well. If it doesn't show up, you may really need to download the fonts.
If you want to really write in Japanese, download this program from Microsoft:
http://www.microsoft.com/downloads/details...&displaylang=enIt comes with the fonts and everything you need to write in Japanese. And you can get more japanese fonts on:
http://www.travelphrases.info/gallery/Font...nese.html#linksIf you're wondering, the standard japanese fonts are:
MS Gothic
MS Mincho
Hope that helps.