correction you could have a 6 core processor with an awesome graphics card and you only put 1gb ram in a comp and your still going to lag.
the memory does allow you to run more programs at a time. BUT it also lets those programs be ran before the computer lags. what i mean is you can run more things before your computer lags even if not all at once 4gb ram is fine and a quad core processor is fine for most games.....but for those that want to have the best comp possible you would want
6 core processor, 16 gb ram, dual 1gb gfx cards, a 40" monitor, and a 2 tb harddrive