Here are the unofficial system requirements for Grand Theft Auto IV for the PC that have been circulating the Internet. While not official, it's a pretty good bet that they are pretty close to what you'll need and compariable to other new games being released.
Software: Windows XP SP2 or higher
CPU: Dual Core Processor (Intel Pentium D or better)
Graphics Card: 512MB Direct3D compatible graphics care or Direct3D with Shader
RAM: 2GB
Hard Drive Space: 18GB available memory
Drive: DVD-ROM (Dual Layer Drive)
CPU: Dual Core Processor (Intel Pentium D or better)
Graphics Card: 512MB Direct3D compatible graphics care or Direct3D with Shader
RAM: 2GB
Hard Drive Space: 18GB available memory
Drive: DVD-ROM (Dual Layer Drive)
