We all need display adapters, it's what deciphers all the coding into text and pictures on your screen. Display adapters come in a variety of flavours to suit different requirements and you need to be sure why you need an upgrade and if your current hardware supports it.
More memory means more colours and higher resolutions and that's about it.
Today for normal cards 4mb is about the norm for most people. Many older monitors cannot cope with the high refresh rates that newer cards take for granted. Also older monitors cannot handle the larger display sizes such as 1280x1024 or above. This is an important point to note as buying a new monitor, although a good investment, can be expensive. With the new breed of 3D accelerated cards on the market, it is becoming a bit of a minefield for buyers to get their heads around the new technical terms that are sprouting up.