I suppose if you have a used PC and it has all of the original recovery disks and driver disks, you can use those.
That's what I do, I aquire old computers from people who have upgraded and I get all of their recovery media, then I just use them to "recover" the original OS and install all of the drivers and original OEM programs.
Sometimes the "Recovery" disk is a Norton Ghost Image, that just re-installs the original OS, sometimes it is a Windows Install Disk, with a built in Key that you cannot add or change, that self-activates and it is made specifically for the hardware on that particular PC, so if you change something major in there, it will fail to activate. The you have to buy a new Key.
You MAY be able to contact MS, ask them for some legit Trial installers, they will come with all of the documentation needed. You have to be in the System Builder Program to get those. The original System Builder program I did was a box full of about 15 Windows 95 installers, keys and those stickers. Those disks are only legal to use with Brand New Systems.
I remember I used to buy non-licensed Windows XP install disks from PC-Club, they sold them for 5 bucks apiece, I would buy my own licenses for those, but I always gave the CD to whoever I sold the system to, I never made copies of it.
I don't know if PC-Club was strictly legit with that practice, they would do it for me cos I was pumping several hundred bucks into their store a month. But then they all miraculously vanished off trhe face of the earth in about one day. One Day, I bought a ton of hardware from them, the very next day the whole STORE was vacant, no warning, not a single clue this was gonna happen:
PC Club Net - The Company