I mentioned the release of PowerShell at:

Tip 10853 » Windows PowerShell 1.0 English update package for Windows Server 2003 Service Pack 1 and for Windows XP Service Pack 2.

AND
Tip 10854 » Windows PowerShell 1.0 localized update package for Windows Server 2003 Service Pack 1 and for Windows XP Service Pack 2.

If you have a previous version of PowerShell installed, the Setup program will NOT install PowerShell 1.0.

If you are unable to uninstall the previous version, you can:

1. Open a CMD.EXE window.

2. Type the following command and press Enter:

REG DELETE HKLM\Software\Microsoft\PowerShell\1 /V Install /F

NOTE: REG.EXE is built into Windows XP, Windows Server 2003, and later operating systems, or installed from the Windows 2000 Support Tools.