In addition to what Hyper said, you could try and find browsers that implement custom font rendering. I'm not sure if there are any but that would cover a lot of reading

Perhaps even a custom port of the open source Chromium... just throwing that in the wind maybe someone already came up with that idea.
One pretty involved solution would be the "seamless" mode in VirtualBox, you could use a Linux browser or try to install OS X in a VM. Then you can seamlessly open the browser on top of Windows. On the plus you'll have it sandboxed. I did not spend too much time in Linux Mint yet but what I saw was very nice. Text quality in VIM and Terminal was important for me and the rendering in Linux Mint was definitely better than Windows. It was softer and quite similar to OS X.
Alternatively you could try to
install Mountain Lion in VirtualBox. Then use dictionary etc in seamless mode? You can even buy ML if you're that inclined it's only 16 €.
EDIT: Nevermind you seem to be more interested in the fonts than the font rendering. Indeed the Japanese fonts look very nice.
See
List of typefaces included with Mac OS X for the name of the Japanese typefaces.
You can probably get ahold of them, however don't expect them to look as good, as Hyperborea explained quite well.