Back in February, 2010, I posted instructions on how to create a bootable USB drive that can install any version of Windows 7. As of yesterday, ISOs of updated versions of Windows 7 with SP1 have been made available to Microsoft TechNet and MSDN subscribers.
If you want to update your install media with the ‘slipstreamed’ version, grab a torrent and then check it against the official Windows 7 SHA1 and ISO/CRC hashes.
The filenames for the 5/12/2011 versions of Windows 7 Ultimate are below.
Windows 7 Ultimate with Service Pack 1 (x64) – DVD (English): en_windows_7_ultimate_with_sp1_x64_dvd_u_677332.iso
Windows 7 Ultimate with Service Pack 1 (x86) – DVD (English): en_windows_7_ultimate_with_sp1_x86_dvd_u_677460.iso