Few thoughts:
I'm not too sure on the PSU, Raidmax isn't known for good ones. Get something
build by Seasonic or Enhance (not necessarily brand name; for example, Corsair PSUs are built by Seasonic) and you can't go wrong. 500W is enouh for that rig, but for future proofing you might consider ~600W. 700 or 750, maybe even 800W if you might plug in a second GFX card in the fututre (SLI/Crossfire). 2x 9800GT is faster than GTX285 (on high resolutions) while costing just a fraction.
It's not really future-proof. DDR3 is the standard and affordable nowadays. AM2+ socket has been superseded by AM3. Get a DDR3 board with AM3 socket and Phenom II to match, and you have a good system with a better upgrade-path.
*If you're considering moving to 9800GTX, have a look at the GTX 260 (with 216 shaders, not the old model). Depending on the brand, they cost the same or a little over the older cards while being faster. As far as Nvidia goes, it's good value for money.
FSX will run fantastic and no compat. problems I can think off.
**Having onboard GFX shouldn't conflict with a dedicated card (just disable the chip in BIOS), but you're better of with a board without it; possibly higher performance and you don't pay for something you don't use.