Isn't a Vaio a laptop computer ? 
Anyway, it's hard to answer your question. In fact, both the cpu and the video card need a serious upgrade.
I think you'd better save a little bit of money and switch to a totally new computer, with modern hardware in it.

- your current cpu is monocore, wich is very bad for detailled sceneries and photoreal sceneries. Also, its frequency is very slow, which is not good for frame rates. You want at least a quad-core, running at least a 3GHz.

- Your current video card is a low-end card from several generations in the past. I don't know about the current namings in the NVidia cards, but anything above the 8xxx generation, with at least 512 Mb of RAM on it, is what you need.

- 2 Gb of RAM are a minimum. You might want 4Gb, with a 64 bit operating system, like Win7 64 for example.

A motherboard supporting a P4 won't allow for a CPU upgrade that would make sense..

The video card was low-end even for its day.. so an upgrade there wouldn't hurt... However, FSX isn't your normal beast...  the best video-card in the world can be useless if the CPU is a serious bottleneck.

A high-end v-card now can of course be used in your next computer, but that same card will be less expensive when you get around to getting a m-board/CPU more suited for FSX.

I'd save for a completely new computer..