I actually had a Dell Dimension 3100, that I got two years ago. I wasn't into much gaming at the time, as I only played Counter-Strike 1.6, which can run well on integrated graphics. I had made about 450 bucks that summer working at my high school, and the day after I got my check, came a Dell magazine, with a Dell 3100, 1gb RAM, P4 3.06 GHz, with 19" monitor for 450 bucks. I bought it instantly. At the time I had little computer knowledge, especially about graphics. I knew 1 gb of ram was ok, and that processor was decent (Dual Cores weren't standard yet). I didn't know it had no graphics card, no pci-e x 16 or AGP slot. It had 1 gb of RAM, not bad for the time, but no more slots, and 2gb maximum. The case was a BTX form factor, a failed design that is uncommon and expensive. The power supply was 230 watts, and the case was just annoying to try to add any sort of part.
The computer was reliable, no real problems (except to junkware they put in it, though I fixed that with the "Dell Decrapifier" application
), and it lasted. It's good for standard use, but don't expect any upgrading, or heavy media or gaming off a dimension.