I'd get the quad core LGA 775 Processors.
Intel Core 2 Quad Q8200/Q8400 are good options.
Q8200/Q8400 are both 1333MHZ FBS.
The problem is that the mobo in the PC I'm trying to upgrade supports 533/800MHZ FBS
What is your motherboard?
Intel 945GC. It came with a Lenovo 3000 J200 9691 34G desktop.