You'll find SP1 in Windows UpdateBy Ed Bott
On March 18, 2008, Microsoft made Windows Vista Service Pack 1 available for general download via Windows Update. Here's what you can expect from the installation process.
Vista SP1 isn't being delivered automatically until mid-April 2008 or later. Until then, you'll have to check Windows Update manually. Click View available updates to see if it's listed.
Read the full report here: Want Vista SP1? Here's what to expect.