And, there is no DEFINITE answer with any one.
Still, there is a good article by Kingston, the Memory manufacturer, which you can refer for your computer's actual memory need so that, it can run comfirtably.
You will see that, except Windows 98, all other modern Operating Systems now need up to 2 GB RAM for Computers that are involved in Multimedia applications.
Moral of the story: Have good memory! A larger memory is always better!