It's only a good deal if it can handle a medium to high end video card.
So first of all, does it have a PCI-e slot? Server motherboards may have them missing due to the headless configuration found on many servers. You'll need one to put in your own card, and that nVidia chip sounds like it might be integrated, so there's no guarantee from the information given that there's a PCI-e slot.
What kind of processor is it, besides being a dual core processor? If it's a Pentium D, then it's not a real step up from your current processor other than being better for multitasking due to having a Pentium 4 architecture. A Core 2 Duo would be twice as fast at nearly half the clock speed. An original Intel Core Duo isn't bad either, but isn't much of an upgrade.
What kind of memory is it? You'll really want DDR2 800MHz (PC2 6400) or better, and preferably the same thing in every slot (for timing reasons). I've been building a new low-end gaming system and things ran much smoother after I replaced the crappy memory I originally stuck in it with some newer stuff (it was failing some stress tests I was putting it through, so I've been replacing parts). DDR3 is better, since it's cheaper and easier to find these days.
Finally, does the power supply have two PCI-e 4-pin connectors and a rating of at least 550W? You'll need that for a video card upgrade. Just having lots of molex connectors isn't always good enough with high end cards either -- I'm finding that out with a cheaper gaming rig I put together, since the "650W" PSU I stuck in it can't handle a Geforce GTX 275. I had to downgrade the machine to an ATI Radeon HD 4830 due to power draw issues. It still plays most games on high settings though.
If it doesn't meet all those requirements, then don't buy it. You'll end up replacing half the parts anyway, just so you can stick a decent video card in it.
If, on the other hand, it does meet those requirements, I've got a spare GeForce GTX 275 I can sell you for $100. You should be able to play pretty much any game on High or Very High at 1920x1080 with this card (I tested it out). It performs somewhere between an ATI Radeon HD 4830 and an nVidia GeForce 460, but it has a really big power draw to it, so you'll need a good power supply with the right connectors.
If you want to buy a new card, the nVidia GeForce 560 is at a real sweet spot in terms of price vs. performance. You can find it as cheap as $180, but it'll be worth it, since it'll play pretty much everything maxed out. Once again, however, a good PSU is essential here.
If you're just looking to play games on Medium-High at more lax resolutions (i.e. 1440x900) and without the big power requirements, the Radeon HD 4830 is a good buy at less than $70. I had to reseat the heatsink on mine though due to glitches, and AMD/ATI's drivers really suck though, especially with OpenGL apps and games.