Generally speaking, more RAM...the better computer functions with heavy tasks like Photoshop, 3-D rendering, video editing.
A powerful video card AND plenty of RAM helps to speed up fps (frames per second) in 3-D games. Also, processor speed also helps, too.
A basic computer user only needs min of 256 MB or more for basic web surfing, e-mails, word processing.
I have 512 MB of RAM with a 733 MHz processor (megahertz doesn't mean anything) the processor and articecture matters the most
also have a ATI Radeon 9800 with 128 MB VRAM