FSX is very CPU intensive, to optimally run FSX you will want to get at least a 2nd Gen i5 CPU. An i5 2400 is good, but a better choice would be to get an i5 2500K (for OCing), allowing the PC to run FSX more smoothly. With the new 3rd Gen Intel Ivy Bridge CPU's arriving May '12 prices should go down soon after for the older 2nd Gen stuff.
Have a good one ,
MAE-PC9: Antec 902 \ Antec Signature 650W \ MS Win 7 64-bit \ FSX \ Flight
Intel 2500k \ ASRock E3 G3 Z68 \ Corsair XMS 8GB DDR3 1600MHz \ Corsair 60GB & 240GB SSD
MSI HD6870 1GB \ Auzen Meridian 7.1 \ LG GGC-H20L Multi-Drive \ WD 500GB, 1TB & 2TB HDD
Samsung 225BW LCD (#1) \ Sony MFM-H65W LCD/TV (#2) \ Sony SDM-X52 (#3)