Trainz Simulator 2009 System Requirements

Minimum System Requirements:

CPU: Pentium IV 2.2GHz (or equivalent) 
RAM: 1 GB
Video: 64MB 3D Graphics Card (NVIDIA GeForce2 or equivalent)

OS: Windows XP Service Pack 2
Resolution: 1024×768

Recommended System Requirements:

CPU: Intel Core 2 Duo (or equivalent)
RAM: 2GB
Video: 256MB 3D Graphics Card (NVIDIA GeForce7 Series or equivalent)
OS: Windows XP Service Pack 2
Resolution: 1024×768

source: Wizoo