The bottom line is that as long as the machine you are attempting to install Windows on to is legally licensed then you can use any copy of the media you like.
However the "version" of Windows that you install must match the license in place on the machine.
So if your machine has an OEM license then it must be an OEM version of the OS you install, not Retail, not Educational, not VLK etc.
So if your friend has a PC with a valid OEM license attached to it (still using original motherboard supplied etc) then you could use your own OEM media, other friends OEM media quite legally.
With regards to SP levels - the license is for an OS release, not for a particular version.
So an original OEM license could be used to install an OEM SP3 installation without any issue - unless the original key was a known compromised one and is no longer accepted after the SP1, SP2 & SP3 releases.
(There were many compromised keys posted on the web, so with each SP release MS have made it so they won't install, basically baring the keys).