What version are you running? 2.0.3 should have some slight performance improvements.
Memory and graphics card are almost certainly not the problem, it's probably the AI scripts. There's some peculiarities around the scripting engine that have been dragging things down. If you press F2 the performance window will appear, with a detailed breakdown of what;s taking so long. I'll try to work in a more comprehensive performance fix into 2.0.4