Well, it all depends on your motherboard, but generally speaking no you can't replace CPUs on laptops. I tried running FSX on my laptop which is nearly the same as yours except my CPU is an AMD Turion 64X2 TL-56 (1.8 ghz) and I also have really cruddy graphics (ATI Radeon X1100 >:( >:(

it's not that your CPU was bad, it's just that it's speed isn't adequate for FSX at high settings, and neither is mine : ). I run FS2004 on my laptop (runs very nicely and NO BLURRIES, plus good smooth multiplayer flying) and FSX and X-Plane 9 beta-2 on my desktop, x-plane 9 runs like a dream (very nice program for only being made by like four guys. Only complaint is that cities are all generic without add ons), and FSX is pretty good too, but I'm still saving up for a desktop that can actually run FSX at pretty good settings and maintain at least 22FPS (see sig)
So basically, the only laptops that can run FSX well are the ones that cost around $6000 or so ;D, you'd be much better off downgrading your software and saving your FSX DVDs and your money for a good desktop. Of course, it's ultimately up to you, but I'm just giving my two cents based on my experience with FSX