Minimum:
Windows XP
Intel Pentium 4 2.0 GHz
512MB RAM
128MB Video RAM
1GB Hard disk space
VGA Monitor with at least 1024x768 screen resolution
Killer Xeno Pro NIC (Network Interface Card) (Lagless gaming solution!)

Standard:
Windows XP/Vista/7
Intel Core 2 Duo 2.2 GHz
2GB RAM
Nvidia GeForce 8400 GS 512MB or ATI Radeon 9600
1GB Hard disk space
22" Monitor (Any brand) with at least 1600 x 1200 Screen resolution
Killer Xeno Pro NIC (Network Interface Card) (Lagless gaming solution!)

High:
Windows XP/Vista/7
Intel Quad 2 Core 3.0 GHz/Intel Core i7-975 3.33 GHz Extreme Edition
4 or 6 GB RAM
Nvidia GeForce GTX 480 1.5GB Video RAM or ATI HD 4890 1GB Video RAM
24" Monitor (Any Brand) with screen resoultions of up to 1900x 1200
Killer 2100 NIC (Network Interface Card) (Lagless gaming solution!)

Above all, Killer NIC cards works best with at least 8MBPS of speed