If you want to get Windows Vista using Windows Update then copy the following in a bat (or cmd) file and run it in an admin console (if you have UAC switched on); then run Windows Update. Also the SP1 is a Release Candidate and not the "final" version so use at your own risk!
@echo off
reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\VistaSp1 /f > NUL 2>&1
reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\WindowsUpdate\VistaSP1 /f > NUL 2>&1
reg add HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\VistaSp1 /v Beta1 /t REG_SZ /d da2ba4db-dedb-437e-8e7e-104643454bb6 /f
IF NOT %errorlevel% == 0 ( goto ERROR)
:SUCCESS
@echo.
echo ===========================================================
echo Windows Vista SP1 registry key has been set successfully.
echo Please check for updates in Windows Update.
echo ===========================================================
@echo.
goto END
:ERROR
@echo.
echo ===========================================================
echo FAILED to set Windows Vista SP1 registry keys.
echo Please run this script by right clicking and selecting
echo "Run as Administrator".
echo ===========================================================
@echo.
goto END
:END
pause
