i tried some time ago to type in japanese on the forum and i don't think it worked very well. you might have to bash it a few times to get it to work. but yes, of course it's supported!
Not really, but they don't have the same type of alphabet - if you don't count romaji. But anyway. Hiragana and Katakana is one syllable for each symbol, Kanji is one word for each symbol.
Well, my computer will sometimes just randomly get me stuck in Japanese typing mode when I'm filling out forms in a web page, including here... usually afterwards I vaugely remember hitting a key by accident.
Works for me. Too bad I don't know any Japanese to type.
On my computer, and I think this is fairly standard, I hit left-alt and left-shift to switch between English and Japanese input. Maybe that's what you're hitting? Only works if you have the input mode installed, of course.
I forget exactly how I did it, but it was part of the XP installation/configuration. I opted to install East Asian language support and we had to install the input method extension (IME) from the CD. Mine is a tablet PC, so this may have had to do with using the stylus to draw kana and kanji (somewhat wasted on me at the moment, but my ethnic-Chinese bf was able to get it to recognize some Chinese words he wrote), but I think the mouse would work too. The IME pad lets you draw in a square and then presents you with a list of possible symbols to choose from.
Try regional and language settings in the control panel and see where that gets you. Once I had the East Asian language support installed I picked out input options; I only bothered getting keyboard input for Japanese because it's the only one I'm likely to type in (the East Asian language stuff also includes Korean and Chinese). So I don't know how multiple Asian language entry is handled.
I may have had to do something similar for Word specifically as well. Kana are easy, although I haven't found a keyboard shortcut to switch between katakana and hiragana, etc (maddening). I haven't really tried to input kanji except with the stylus (and very little of that) since my main use of all this is to transcribe bits of Japanese from games or books and paste them into a translator or doc, so I'm usually looking up kanji using Jim Breen's multiradical lookup and copy/pasting: 朱色
Sorry this is answering a lot of stuff you didn't ask and not what you did ask. I was working with a brand-new computer and its original OS and don't really know how to answer your question directly.
Me? Primarily IE, occasionally Mozilla. I typed my above post on my laptop, which has an IME installed; this one is on my work desktop, which has Asian fonts but no input. However, I seem to be able to copy/paste Japanese in either browser. I do note that previewing in IE shows it as a code in the typing window even though the preview itself is fine.