When choosing a video card, it is important to know what you'll be using.
The cheapest route is to find a motherboard with a built into it. This is sufficient for most users. If you just do not want one built into the motherboard, or can not find one, almost any cheap video card will do for everyday use.
If you are in game, there are a lot of factors that make a video card "gaming" of quality.
Memory - Video Card memory available (RAM) built in the card you used for your calculations. This is the primary sales trick when it comes to most video cards, but simply having a lot of memory on the card is not going to make decisions faster, but it also depends on what type of memory is currently DDR be the best. Another factor in the memory is the number of bits that is running on, the higher the better.
Interface - The interface is the technology used on the card to connect to the motherboard. The motherboard has to support the interface of the video card you are using, or simply not work. There are lots of different types of interfaces now, PCI, AGP to PCI Express, and there are different variations of AGP, and AGP 4x, AGP 8X, etc AGP interfaces are usually compatible with earlier versions, but not so broadly consistent with the versions, so you can put a card in a 4x slot 8x, but not vice versa. They also are not cross compatible, so you can not put a PCI Express card in a regular PCI slot, or AGP slot.
Interfaces also regulate how fast the card can be. PCI is the slowest, then AGP expansion of the different versions of AGP, and the currently fastest PCI Express, which is used in most video cards today's high end.
Other factors you may want to consider that do not necessarily have anything to do with speed:
Resolution - How large of a screen of the video card can display. If you have a very large screen, you'll want a card that can be displayed in higher resolution.
Outputs- The types of connectors that the video card must be connected to a monitor. VGA is the most common, but it is the lowest quality. A lot of monitors, especially LCD monitors, DVI support now, which is a higher quality production. Some also have S-video outputs, or possibly one of each, or grouped together, which leads us to whether it can support multiple displays.
Multiple Display Support - regulated or not the card can show multiple monitors at once. Some cards have multiple connectors on a single rate, others will have several different types depends only on the card. Although most cards with multiples of the same type is likely to support multiple monitors, which have several different types do not necessarily support multiple monitors. Windows XP has native support for stretching the screen on multiple monitors, so you just have to find a card that supports it.