Q: Can I slipstream Service Pack 1 into my Windows 7 or Windows Server 2008 R2 image?

A: The installation of a service pack into an offline image of Windows 7 or Server 2008 R2 is not possible because of changes made in Windows servicing starting with Windows Vista. Versions of Windows Server 2008 R2 and Windows 7 with SP 1 is available on MSDN and TechNet now.

If you have a custom image for your organization, you need to recreate it with SP1 installed. Ideally, you can use something like the Microsoft Deployment Toolkit or System Center Configuration Manager to create your images, which will automate the process and make it simple to re-create your corporate images whenever service packs are released.