512MB are enough to play 720p video with a good video card and good mpv/mplayer settings.
I think even 128MB would be enough under cwm+mplayer if the iGPU is at least from 2006/7.
For games, meh. Nethack, Slashem, IF (frotz), MSX emulators with the Metal Gears and the Konami Games, and Mednafen.
Much more interesting would be an old computer disconnected from the internet. 512mb is enough to get away with it if you're not crazy with your desktop environment although it would be tight now even for fairly conservative people.