My advice, if it doesnt have dedicated graphics then Vista is just going to eat to much resources to make game play "playable"...
However, yeah FSX will run under Vista on this machine, not sure how far the sliders will go up though untill you start loosing to many frames per second that the game is to jerky and not really playable, my prediction is not very far up...
My partner has Vista on a very similar spec machine, but Turion X 2 and not intel, and i had to remove it as it wasnt going well at all...
FSX will run at Minimum slider levels on fairly low spec machines, so it really depends on how much graphic acceleration you are after...