Metin2 runs flawlessly on a 2 years old computer bought at Staples for 300$. At low settings, yes, but the game is still a 3D game that looks alright, and everything is smooth, even though the system basically can't run anything else that's in 3D.
Knight Online works well too, although not as smooth as Metin 2. Stay away from the 400 persons Lunar Wars, though.
Turf Battles has relatively low requirements, but still a bit higher than Knight Online.
