Basically this is classed as a eroge (hentai game) for the pc as of 2002, however the game itself only has marginally more sex than god of war as a trilogy has, but much more tasteful. Unfortunately i'm counting this as 18+ for playing the game, for shame if you don't but it's already pirated so oh well.
You'll want winrar to open the basic files, magicISO and an english fan-patch to actually be able to read it (it was never released outside japan)
Links will be at the end if possible.
Winrar is used to download and extract files from .rar files, these present themselves as three different colored books bound by a leather strap.
* Download the winrar files 1-5
*with all the files downloaded, pick the first and extract to desktop/your own folder/ ect.
*Select magicISO via right click (stands in the same mini bar as volume control and internet connection)
* in the R-click menu find the 'virtual CD/DVD-ROM' button, which should be at the top of the list.
* hover your mouse over the empty selection and click mount
*Find the folder/place where you extracted the game from there and it'll be mounted (acts the same if you put the disk in physically)
*DON'T run it yet! Select your language patch and load it
*when prompted, pick the disk (should be E:/) and it'll take a 1 time bond
*select the disk and play
Game files 1-5- http://erogedownload.com/downloads/utawarerumono/
English patch 1.1- http://mirrormoon.org/node/239