well, seeing that you'll need a whole new system, you can't upgrade just the motherboard. also, you mentioned you don't have oodles of money to just blow on new hardware, so let us know what kind of budget you have for a new system build and we'd be able to help you a bit further

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but, without knowing, here's what i would get for myself now.....you could probably go along the same lines
intel p35 chipset or NVIDIA 780i chipset motherboard
intel e8400
2GB of RAM
8800GTS 512MB video card (you can get two of these if you go with the 780i and your pocket can spend the extra cash)
600w PSU (minimum wattage)
2x150GB Raptor-X HDDs for RAID 0 config
SATA DVD burner
other than that, you still need other peripherals, like a monitor, keyboard, mouse, and speakers