Minimum:

Supported OS: Windows 2000/XP
Processor: Pentium® III 733 MHz or compatible (Pentium® 4 1.2 GHz or compatible recommended)
Memory: 128 MB RAM; 256 MB for XP (256 MB; 384 MB for XP recommended)
Graphics: Any ATI Radeon™ or GeForce™ 2 with 32MB or higher; or other video card with 32MB and hardware T&L (ATI Radeon™ 64 MB SDR or GeForce™ 2 Pro or other video card with 64 MB or more memory and hardware T&L recommended)*
DirectX Version: DirectX® version 9 (included) or higher
Sound: Windows® 2000/XP-compatible 16-bit sound card*
Hard Drive: 600 MB free

* Indicates device should be compatible with DirectX® version 9.0b or higher.

RollerCoaster Tycoon 3: Platinum screenshots