Civilization IV: Beyond the Sword

Windows 2000 (plus Service Pack 1 or higher), Windows XP Home or Professional (plus Service Pack 1 or higher), or Windows Vista; 1.2GHz Intel Pentium 4 or AMD Athlon processor, 256 MB RAM, 64 MB video card with hardware T&L (GeForce 2, Radeon 7500 or better), DirectX 7 compatible sound card, 1.7 GB of free hard drive space, DirectX 9.0c (included)
1.8GHz Intel Pentium 4 or AMD Athlon processor or equivalent (or better), 512 MB RAM, 128 MB video card with DirectX 8 support (pixel and vertex shaders), DirectX 7 compatible sound card, 1.7 GB of free hard drive space, DirectX 9.0c (included)