Web browsing in Japanese presents several choices. You can use Shoudoka, a free online service which interprets Japanese web pages and spits out the kanji and kana through images you can load, you can set your browser up to display Japanese fonts, or you can use a viewer program (see below).
Shoudoka is rather nice if you just want to view web pages without downloading or installing anything. You go to the Shoudoka homepage at shoudoka.com and give it the URL of the page you want to see, and it will read it and give you a version where all the kanji and kana have been replaced by images. It's free, it works beautifully. The downside is that you have to load in the images, but they're kind of small, so unless the page has every kana and a whole bunch of kanji that's not too big of a deal. Also, you can only read web pages this way, not e-mail, news, or in fact anything else.
Once you've downloaded these fonts, run the program and the font will automatically install
itself. If you download a .ttf or similar file, you'll have to put it in Windows' fonts
directory; under Windows95, this is c:\windows\fonts or c:\win95\fonts (you get the idea).
Next, open up Communicator, select the menu Edit - Preferences ..., and go to
Appearance - Fonts. In the "For the encoding:" box, click the box and select Japanese. Now,
under "Variable Width Font" and "Fixed Width Font", select the fonts you want to use. I happen
to like MS Mincho for Variable Width and MS Gothic for Fixed Width. Of course, this means I
have two VERY large font files in my font directory. You could just get one and use it for both
settings. The upside to this is that you can view pretty much any Japanese on webpages,
e-mail, newsgroups, what have you, without having to remember to load up a viewer program. The
only downside is that the fonts are kind of big and so take a couple seconds to load the first
time you open a Japanese-encoded file. Also, these instructions are only for Netscape
Communicator. If you have an older version of Netscape (say, 3.1), then there's a good page
you should take a look at
here.
Microsoft designed Internet Explorer with the idea of being able to extend it in ways like this. If you look around on the Internet Explorer page at microsoft.com you should find a Far-East extension pack for it. Alternatively, you can look at Patrick Cyber Domain which has tips on how to "extend" Netscape and IE to view Japanese.
There are two main viewer programs that I know of, KanjiKit and NJStar's viewer. Both support most CJK encodings, and run in the background while you work. Both will display/print Japanese text almost anywhere (except in the title bar of a program, it seems ... in fact, my Netscape won't print Japanese text without KanjiKit, even if it's a Japanese font on a Japanese page ... ) I've tried both programs, but tend towards KanjiKit just because it's what I'm used to. However, it has one slight downfall: it doesn't auto-detect the encoding of a document like NJStar's does. That means if the output comes out wrong, you have to click where it says "EUC" or "SJIS" and try to figure it out yourself, but that's not a big deal. Both programs are commercial, but have free trial periods. NJStar can be found here and KanjiKit can be found here.
Even if you use a viewer program, you can't type in Japanese text (well, actually, KanjiKit does let you type in Japanese text ^_^; ). So, if you plan on seriously using Japanese on your computer and you don't have a Japanese system, you should get a Japanese word processor. One such program is JWP, a freeware word processor which is, in fact, what I use. It has nice kana/kanji conversion utilities, can read/write JIS, SJIS, and EUC text, and has nice kanji lookup facilities. Also, if you have EDICT, it can search through that for you, so you end up having a really nice freeware suite. JWP is available from the dictionaries section of Jim Breen's Nihongo FTP site, reachable from my links.
Another word processor is commercial, and somewhat pricy. It's also by NJStar corporation, and (I believe) has a shareware version with a thirty-day trial period. I haven't used it, though, so I can't comment on it.
A popular free Japanese dictionary is Jim Breen's EDICT format (which just got a new release!). The way this works is you download the EDICT dictionary files, then download a dictionary program. For DOS, you download JDIC, and for Windows there's WinJDIC. Both programs are rather nice (which makes it too bad my version of WinJDIC bailed out on me), but JDIC is slightly differently featured from WinJDIC: the main difference is that JDIC does not output romanji. All it puts out is kana and kanji; you have the choice of what you want to read with WinJDIC. Both programs read from their own kanji fonts, so you don't have to have MS Gothic/Mincho installed, but you DO have to pick up different kanji fonts. Also, JDIC (the DOS version) supports using more than one dictionary file, so you can also search through, say, the ENAMDICT name dictionaries. The EDICT files, JDIC, and WinJDIC are all available at Dr. Breen's FTP archive.