These are the requirements floating around the web at the moment for World of Warcraft Cataclysm. Unless Blizzard say otherwise we will go with these.

World Of Warcraft Cataclysm minimum system requirements:
Windows XP 32bit (SP3), Windows XP 64bit (SP2), Windows Vista 32bit (SP1), Windows Vista 64bit (SP1):
Intel Pentium 4 1.3 GHz or AMD Athlon XP 1500
1GB or more of RAM
NVIDIA® GeForce® FX or ATI RadeonTM 9500 video card or better
DirectX-compatible sound card or motherboard sound capability
25 GB free hard drive space
You must have an active broadband Internet connection to play

World Of Warcraft Cataclysm recommended system requirements:

Windows XP 32bit (SP3), Windows XP 64bit (SP2), Windows Vista 32bit (SP1), Windows Vista 64bit (SP1) Windows 7:

Dual-core processor, such as the Intel Pentium D or AMD Athlon 64 X2

2 GB RAM (2 GB for Vista users)

3D graphics processor with Vertex and Pixel Shader capability with 256 MB NVIDIA® GeForce® 8600 or ATI Radeon 2600 or better

DirectX-compatible sound card or motherboard sound capability
Broadband Internet connection
Multi-button mouse with scroll wheel recommended