I have a legit Windows 7 Home Premium (x64) OEM disk and key (without SP1), and updated to SP1 online some time ago.
I now wish to re-gen the system to produce a cleaner operating experience (get rid of a lot of the unnecessary junk that I have accumulated). My neighbour has a legit Windows 7 Home premium x64 disk, newer since it includes SP1.
Can I use his disk to install on my PC, use my legit key, and get the benefit of already having SP1 without having to go through the experience of the two-step process (original, then update to SP1) with my CD? Not a big deal, but a valuable option for the bandwidth-challenged consumer.