If you need to create images that include SP1 or just want to have a copy of the full service pack, you can grab it at this link (warning – it is 1.9g in size)
Service Pack 1 for Windows 7 and Windows Server 2008 R2 Landing Page
You can also fire up Windows Update and grab the Service Pack that way, In fact, if you have been keeping up to date through Windows Update, the download is actually pretty small. For my laptop (running Windows 7 Ultimate 64bit) it was only 77megs. I would recommend going this way for one off machines and every day consumers.