I memorized the win95 one (legit copy) which was easy since it was just digits (and I was way younger). It ended in 18805 iirc. Win98 was a copy from a friend and already had letters, much harder, but I eventually memorized that to. It started with g3pdy bdkv7.

Now that I think of it, a non pirated OEM windows key would have made for a great password. ;)