I'm too fucking lazy to read through all that, so I'll just copy my standard answer and past it here. Don't worry, it works every time.
1. Download all the parts.
2. Once you have all the parts, use winrar to extract part1 (it will automatically extract all the parts). If you don't have winrar, Google it.
3. If it's an ISO files, mount the disc with Daemon Tools. Read this and this.
4. Before you install, you need to change you locale. (You only need to do this once.) Read this. This is very important if you want to play Japanese eroge. If you skip this step, I'm afraid you can't play most of the game in here. Eroge is originally made for japanese people, so it's very normal to change your locale into Japanese.
5. Install the game.
6. Crack it if it needs a crack. (Always read readme/installation note if it has one.)
7. Apply the translation patch. (If it has one.)