Video Memory

It's the display adapter or video card. The video card is an expansion board responsible to convert the images created in the computer to the electronic signals required by the monitor. In other words it's the part of the PC that let you see data as images on your screen.
Each Video card has its own memory (RAM) that act as a buffer. The newest Video cards can have a memeory up to 256 MB. Your video card memory does not support the graphics of the game that you're playing. You can see the size of your video card memory when your PC boot, and also you can see it by:
click Start/All Programs/Accessories/System Tools/System Information. In the left panel click the + sign of Components and click Display. Now look in the right panel and see Adapter RAM and check the size of your card memory.

Now to play the game, first go to read file in the Game CD, and look for system requirements, and you can see how much video memory do you need to play the game.

In general, you need to change your video card to 128 MB one in order to play most of today games.