For sake of clarity.
You have a Core2-based system. It'd be somewhat hard to find a new mainboard for one, and in any case it's a "dead end" to put money on.
The mainboard I've linked there, would take up all your remaining components (old DDR2 memory, GPU, power supply, disks, etc) and should fit into your existing case, though I'm not sure if the Dell front-panel LEDs and switches won't have some weird custom connector (but if yes, you'd have same problem with any other non-Dell mainboard).
However, it'd need a new AMD AM3 or AM3+ processor.
The reason I suggested this one is that you could in the future "upgrade parts as you go", replacing DDR2 with DDR3, GPU with a better one, maybe CPU, then get a new (AM4?) mainboard that'd take your next CPU and other components... i.e. make smaller investments once in a while, instead of paying for whole new computer every couple of years.
However, Pontos pointed out that this mainboard is based on an out-of-manufacture chipset, which might not be the best choice.
And you said you would want to buy a whole new PC in a few months.
So finding a used mainboard for Core2 that fits, or a matching Dell refurb mainboard, might be a good cheap way to re-animate the current PC.
The big question is - which way would you want to go?