This post is awesome. My Windows Seven virtual machine will finally fit on my usb key. I just copy the commands here for the record, and I group them so they can be easily copied to a .bat file.
REM Stop and disable Windows Installer and Windows Module Installer services sc stop msiserver sc stop TrustedInstaller REM Backup ACLs for WinSxS folder (see icacls), so we can restore later icacls "%WINDIR%\WinSxS" /save "%WINDIR%\WinSxS.acl" /t REM Take ownership of WinSxS and subfolders takeown /f "%WINDIR%\WinSxS" /r REM Grant full rights on WinSxS to your user icacls "%WINDIR%\WinSxS" /grant "%USERDOMAIN%\%USERNAME%":(F) /t REM Compress WinSxS files and sub-folders compact /s:"%WINDIR%\WinSxS" /c /a /i * REM Restore ACLs for WinSxS folder we saved earlier. icacls "%WINDIR%" /restore "%WINDIR%\WinSxS.acl" REM Restore Windows Installer and Windows Module Installer services sc config msiserver start= demand sc config TrustedInstaller start= demand