That link has a DualCore E5200?
Looking at the case, it doesn't even look like you'll be able to fit a GPU in there anyway. The x16 slot is right at the top, and doesn't appear to have room for even a single-slot design, let alone anything that runs you to dual-slots. The PSU is also a non-standard dimension, so you're looking at a new case + PSU + GPU as a minimum to be able to do anything with that setup..
IMO, it's just not worth the investment.
**EDIT** Ok, so it looks the same, but oyu have a C2Q8300. I'd be very surprised if you could fit a GPU in there.
Would need to be half-height, and likely a single slot design to have any chance..... and on the OEM 220W (8-9 year old) PSU that's non-standard in it's layout...