How would this computer run WoW? (How would the lag be and how much lag do you get with what amount of RAM?)?

Not very well. I wouldn't try it. My friend has a 6200gt and a Pentium 3 and it lags bad. With that laptop I don't think you could play WoW. 512 mb isnt that bad but because your video and cpu are under the require specs, ram wont help.