There are a four main things you need to know.
1) You will need a new PSU (power source unit) The only one made for the Dell Dimension E310 is the Silencer 470 made by
www.pcpowercooling.com for Dell systems. DON"T buy a Psu anywhere else. They don't fit Dell machines. Price $99.99
2) You will need the best PCI video card that the Dell machine will support and the one I bought--the Radeon X1550 for $89--will work for you.
3) You will need to know the specs on your computer (memory size, cpu speed, hard drive available space, CD Rom availability, as well as the specs off whatever video card you buy. Go on-line to view specs first at which ever place you want to purchase the card.
4) Then you need to check the back of the box (or side of the box) of the games you WISH to purchase. You need to make sure that your new video card (and computer specs) meet the minimum system specs recommended to play the game. If they don't match up, don't buy the game; it won't work.
5) Upgrade your memory to at least 1 gig. Check
http://support.dell.com/support/edocs/systems/dim3100/en/sm/specs0.htm#wp1052310 to see what type of memory you need to buy. Memory must be purchased according to the computer's specs. Will probably cost $60 at Tiger or NewEgg.
The Psu and Video card mentioned above will probably play most games made before 2003 and a number of the games made from then to 2006. There will be many games made in 2006 and 2007 that will not run on your "upgraded" computer. I think that all of the city building games will; that's what I play most. I'm not into "shoot-em-up" games which really take lots of power and computer space. You should be able to play the original Worlds of Warcraft.
You will need to study the directions carefully regarding installing the psu, memory and video card. You can burn out new equipment and/or some of the old if you're not careful.
If you find that the up-graded system won't play the games you want to play, then don't up-grade the old computer. You'll need to purchase a new one that has the specs to play those games. And you probably won't find a new computer with those specs in a store such as Walmart, Best Buy Target or the like. You will need to go to a specialized store such as Tiger.com and NewEgg.com. There are a number of other online stores as well. Phone and talk with a salesperson. You will probably need to spend $700 for a minimum computer to play most of the latest, most popular games. Heavy-duty gamers spend thousands. And they learn to build their own systems. Building your own is not as difficult as it once was.
If I've left anything out, I'm sure someone else reading this post will help you by putting in their 37 cents worth.
Hope this helps.
DD