...i remember working on one of those...tooless on those was nice...easy to take apart and get back together but yea, may only take minor upgrades without a psu upgrade, and it seems as if it will take a c2d at the most...which isnt alot by todays standards, but may be enough to move data from a decent gpu...
read up...apparently someone even fit a q6700 in a e520....so you may be good, check out the machines support page...read up a bit on it.