The new language supports features like pipelines (dir | more), command line calculations (11gb/700mb or 2*2) and even recursive commands (get-process p* | stop-process) - something that you have either seen in Unix or third-party addons like MKS Toolkit or Cygwin Utilities.
Windows Powershell 1.0 was just announced at ITForum in Barcelona. It is free and available as a separate download for your Windows copy.
Alex of Windows Vista blog has a more simple definition of Powershell. He describes Powershell as "If you haven't heard of Windows PowerShell before, think of it as an integrated version of the Windows Command Prompt (cmd.exe) and VBScript."
Though the old MS-DOS style command prompt will still be available in Windows Vista, Powershell could ultimately replace cmd.exe as it matures in the hicoming months.
Download Windows Powershell for Windows XP