I'm asked about tech advice and gaming suggestions very often by friends and fellow fraggers around the world. Since I'm only one man, with two hands and a single keyboard in front of me, I'm going to go ahead and answer one of the most frequently asked topics I've ever been presented. They usually sound something like this:

“Hey, I'm going to go ahead and build this uber-gaming computer. I know practically nothing about this stuff, but I got the money to spend. What should I buy?!”

Now, to be honest, that's a question that could take pages to write up, and I just don't have the time to explore all the complexities of such a thing. However I can help you narrow this down and look into the key factor of a great gaming rig: the video card, or GPU. So, here we go!

Earlier in my 'Computers 101' post, I talked about the basics of a computer system, which are the processor, hard drive, and the RAM. Well, in the case of a computer built for gaming, there is really only one major thing you should be aware of when buying and building parts together: the video card, or the graphics-processing-unit (GPU). The video card separates all of the visual work (aka, what you see) of a computer system, and processes it entirely by itself. This is why heavy use of 3D environments, like in modern gaming, practically require the capabilities of a GPU apart from the computer system. Once a computer has a video card, you're able to tackle a wide range of games both old and new.

INTERFACE
So, the first thing to look at when buying a video card for your system is what hardware you already have, or plan on getting soon; specifically, the motherboard is a key factor. The GPU connects to the motherboard through a certain interface standard. If this is a new computer system, the interface will be a PCI-Express (PCI-E) slot, size x16. If you're computer is from before the year 2005 and you're adding a card to it, the interface slot may be either PCI-E, AGP, or PCI. The AGP interface was being phased out from new motherboards as an older interface standard since 2004. If your motherboard has an AGP slot, you may still be able to find a video card that supports this standard from one card manufacturer, ATI. For more information on how to identify your interface slot, look here. Some older motherboards also support a standard PCI interface instead of both AGP or PCI-E, and if you have just PCI slots you may still be able to find video cards via trustworthy online shops, like NewEgg. If you have a motherboard with a PCI-E interface, you'll be enjoying a much broader selection of hardware for your computer!

PRICE/NEED
In my opinion, the price of the hardware, and the necessity of such a piece, should be the biggest factor in deciding what to buy. If you're building a gaming computer, then usually the video card should be your most important, and most expensive, hardware for your build. Nothing affects a gaming experience as much as the video card. So, if you want the best, you'll have to pay for the best. But if you're just looking for something that's fun and impressive, but reasonable, then you're still in the market for a good GPU. Just remember not to go over your budget, and buy what you need, not something that's overkill.
Speaking of overkill, one way to determine a good purchase is by considering your screen or monitor size, the resolution you'll be playing at. If you're using an LCD monitor that has a native resolution equal to or smaller than 1440x900, you probably won't need a card that has more than 512MB of onboard memory (the onboard memory is like dedicated RAM just for the card). If you're monitor has a resolution higher than 1440x900, then you should need at least 512MB of onboard memory!
Once you've determined that, then start looking for cards that meet both those memory requirements, and your budget-within-reason.

When shopping for such a card, I'd recommend trying to stay with some of the latest video cards available on the market. For instance, if you're shopping for Nvidia hardware, get either their 8800-card series or newer, which include: the 9600-9800 series, and the new GTX 200 cards. If you're shopping for ATI hardware, avoid anything older than the Radeon 3000-card series. Which means, you should look at both Radeon 3600's, 3800's, 4600's, and 4800's. If I were to buy today, the price range of these video cards are from around $100 to $650 or higher, depending on brand name and setup.

The last thing to be aware of when doing this to an older computer, but still equally important as when building a new one, is your card's power requirements. Every new card should be expected to require a separate and direct hook-up to the power supply (PSU) of your computer. If you're building onto an old computer and this is your first time doing this, then most likely you'll need to buy a more powerful PSU in order to avoid cooking your hardware in the process. Check the card's requirements in regards to the PSU, and shop for a new one that goes above them within reason. Also, be sure the PSU has the necessary hook-ups to interface with the card, they will most likely. If you're unsure about your choice of video-card, PSU, or anything else, you could always seek help from a techie friend you know personally, or search for some advice online, where most people like me are willing to help guide you in the process.

Here's a basic checklist on what to go through:
-Interface (AGP, PCI, PCI-E)
-Budget (~$100-$650)
-Memory (512MB or more)
-Power Supply (check card requirements)

That should be it, so good luck on your shopping!