IntelR) G33/G31 Express Chipset Family or NVIDIA Geforce FX5600

Better but not much, the FX5600 is a poor card, that's essentially a DX8.1 card.

Have you checked what your Mobo supports, I'm surprised that your G33 based mobo would be AGP and not either PCIexpress or just plain PCI with no graphic adapter slot.

Really there are better AGP options for about $40 and much better PCIe options for less than $20.

So yes the FX5600 is better (especially because it frees up system resources) but it's still bad.

You may also be held back by your core system too since FSX is very resource heavy and like fast CPUs.