IGN has confirmed that GTA IV has been delayed by two weeks for the PC.  The release date is now set for December 2, 2008.

IGN has also released the PC requirements for GTA IV (along with 6 new screenshots; see link below):

Minimum System Requirements:

OS: Windows Vista - Service Pack 1 / XP - Service Pack 3

Processor: Intel Core 2 Duo 1.8Ghz, AMD Athlon X2 64 2.4Ghz

Memory: 1.5GB, 16GB Free Hard Drive Space

Video Card: 256MB NVIDIA 7900 / 256MB ATI X1900

Recommended System Requirements:

OS: Windows Vista - Service Pack 1 / XP - Service Pack 3

Processor: Intel Core 2 Quad 2.4Ghz, AMD Phenom X3 2.1Ghz

Memory: 2 GB (Windows XP) 2.5 GB (Windows Vista)

18 GB Free Hard Drive Space

Video Card: 512MB NVIDIA 8600 / 512MB ATI 3870

Link: IGN Article