If 5years is how long it must last, I suggest going with a quad core, not a tri-core. I would also suggest grabbing an Intel quad over an AMD, as the Intel's are a hair faster, and OC a touch better if you grab a 45nm version. Not by much, but every little bit counts if it has to last 5 years.
$800 is a tough budget to work with if you have to buy a case and a monitor, but it can be done.
“What the hell did you expect? Leave Vista under the pillow and the OS fairy would make it Win7?” -El Fiendo
“And Bring Mailman back god damnit, he is the Eric Cartman of TPU” -MRCL