Microsoft released Windows 8 Consumer Preview few days back and if you have installed it in your computers and facing issues with your Nvidia graphics card driver or AMD video card then you need to update the Card drivers to the latest version which supports Windows 8 Consumer Preview.
For those having issues with Nvidia graphics card driver then Nvidia GeForce R295 version 295.73.The latest version of Nvidia GeForce R295 is available for 32-bit and 64-bit version of Windows 8 Consumer Preview and is available for a free download from Nvidia official website.
Download Nvidia GeForce R295 version 295.73 for Windows 8 Consumer Preview
For AMD video card the latest version AMD Catalyst Driver 8.93.7 RC10 supports 64bit and 32 bit version of Windows 8 Consumer Preview on following mentioned cards-
AMD Radeon HD 6000 Series
AMD Radeon HD 5000 Series
AMD Radeon HD 7000M Series
AMD Radeon HD 6000M Series
AMD Mobility Radeon HD 5000 Series
AMD A-Series APU
AMD C-Series APU
AMD E-Series APU
AMD FirePro Series
AMD FIrePro 3D Series
Download AMD Catalyst Driver 8.93.7 RC10