Hmm I've had a look and it's obviously a custom motherboard so it probably won't be able to run a quad (even though technically the Intel chipset they used will support it).
My recommendation would be put together a newer machine if you can afford it- you can re-use your hard drive and optical drive, and you can probably get away with transferring the windows licence if you have the disk for it (you'll need to call microsoft and tell them the motherboard died and they'll activate it again).
You'd need a new motherboard, cpu, memory + the graphcs card. You'll probably also want to pick up a new case + PSU.
If that is too much money- you can still pick up the graphics card and it will probably run ok (ish), and transfer it to the newer machine when you have more cash. The other thing to considder- the power supply in that machine will be pretty weak. The 250X might be pushing it a bit (as it requires an external PCIe connector). An HD7750 or a Geforce GTX 750ti might be better options as those are each companies respective fastest cards without the need for additional power (the GTX is the faster of the 2 btw).