Sorry for sounding stupid, but can someone explain to me why his dual core processor with 4 Gb RAM would be slower or worse than my 4 year old P4 with 2Gb. Which actually can run FS2004 fully maxed out at 24 FPS everywhere?
Chances are, it wouldn't.
The memory shouldn't be of much concern, I doubt FS9 goes anywhere near 2GB RAM to start with. Nearly 1gb of their memory is reserved towards graphics anyway.
As for processors, the clock speed is not a show of performance. 1Ghz just means '1 billion cycles per second' as you probably well know, but that does not mean that each cycle is efficient or does much. A very very vague way of understand it is like this: Which goes faster: A car in 1st gear at 2000RPM, or a car in 5th gear at 1500RPM? (Let's not get too technical, you'd obviously have to get up to speed to be in fifth gear anyway).
So in that example, although the engine was going slower (fewer Hz) the speed of the car would remain higher. Fuel efficiency would probably be higher too.
So a modern, slower, processor can be better because it is more efficient
with each cycle. Dual cores means that information can be processed in parallel, so if one core is dealing with a certain task, the other core will handle other tasks at the same time.
It gets complicated, but that's the simple version. The more complex version is like a hopscotch grid where at random you have to go back to the start. A more efficient processor would have a shorter grid (5 steps or so) than an older, less efficient, one (10 steps). There's a better chance that you'd get past the hopscotch sooner if it were 5 steps long than 10 steps. On the 10 steps one you'd have to sprint it across and hope you make it to the end before getting reset to the start. Hence, a faster clock speed and more heat. More efficient = shorter pipelines (hopscotchs) so it can afford to go slower.
Phew.