From a readme:

Minimum System Requirements
• A version of Microsoft® Windows® 98SE/ME/2000/XP
• Pentium® III 1.0GHz (1000MHz) or Athlon™ 1.0GHz (1000MHz) processor or higher
• 256MB RAM
• 8x Speed CD-ROM drive (1200KB/sec sustained transfer rate) and latest drivers
• Full installation of Rome: Total War is required for this patch
• 60 MB of uncompressed free hard disk space for patch update
• 100% DirectX® 9.0b compatible 16-bit sound card and latest drivers
• 100% Windows® 98SE/ME/2000/XP compatible mouse, keyboard and latest drivers
• DirectX® 9.0b
• 1024 x 768 Monitor Resolution
• 3D Hardware Accelerator Card Required - 100% DirectX® 9.0b compatible 64MB Hardware Accelerated video card and the latest drivers*.

ATI® Radeon® 8500
ATI® Radeon 9000
ATI® Radeon 9500
ATI® Radeon 9600
ATI® Radeon 9700
ATI® Radeon 9800
All Nvidia® GeForce® 3 and higher
Important Note: *Some 3D accelerator cards with the chipsets listed here may not be compatible with the 3D acceleration features utilized by Rome: Total War™. Please refer to your hardware manufacturer for 100% DirectX 9.0b compatibility.
Multiplayer Requirements:
• Internet (TCP/IP) and LAN (TCP/IP) play supported.
• Internet play requires broadband connection and latest drivers.
• LAN play requires network interface card and latest drivers.