You can purchase and download the game through these official platforms:

Offers a DRM-free version, meaning you don't need a launcher to play after downloading.

Provides both a DRM-free download and a Steam key. Installation Guide

2.2 GHz CPU (Intel Core 2 Duo E4500 or equivalent). Memory: 2 GB RAM. Graphics: NVIDIA GeForce 7600 or ATI Radeon HD 2400. Storage: 1 GB available space. Train Valley - GOG.com