Icrontic has posted a preview of Windows Preinstallation Environment, which is basicly WindowsXP which you can boot from a CD. The OS has a number of restrictions and is only available to system builders.

As Microsoft states: "Windows Preinstallation Environment (WinPE) is a minimal Win32 subsystem with limited services, based on the Windows XP Professional kernel running in protected mode. It contains the minimal functionality you need to run Windows Setup, pull an operating system from a network share, automate basic processes, and perform hardware validation."

Full preview here