About the only thing that would make it struggle with that set-up, would be the autogen scenery on full tilt. You'd probably get away with it up on about half before it would start to complain, is my guess.
A lot will depend on what screen resolution you can live with too, of course.
Although I still mainly use FSX on my desktop, which is a single-core 3.2 GHz P4 running XP with a pci graphics card, it does definitely run better on my (Vista OS) laptop with a dual core processor and no flashy graphics card at all. Both these machines have 2 gigs of RAM and I did notice a significant improvement on BOTH rigs with the patch. There was a lot of stuff optimised in it, and it seems the FSX doubters were somewhat premature in dismissing the notion that it wouldn't run any better on Vista or dual core, because it does, simple as that, it did before the patch too.
I can confirm that load times were significantly cut after the patch, it was initially somewhat ludicrous, you could go away and make a coffee and when you came back to your PC it would still be loading the flight, but that is no longer true since the patch, it does load a lot quicker these days.
There is still much to be said for FS9 however, and whenever I'm reviewing anything that is suitable for both (for AVSIM), I'll do a lot of the testing in the older sim, purely because it does still load quicker than FSX, and you have to load a lot of different flights to do a decent review.
Nevertheless, when it comes to reviewing what the thing actually flies like, there is no comparison, FSX is markedly better at conveying flight than FS9, owing to its superior air mass modeling, and that alone makes it worth having, but it will be a while before FS9 disappears off my drive for things such as airliners, where the need to feel affected by every single bump in the air is not so great as it is when tootling around in a Piper Cub, or a glider.
Chock