Hi Ugo,
I am running FSX with SP2 on Vista 32 Business with DirectX9 - I don't have a DirectX10 capable graphics card. SP2 has solved many issues and is also a better performer.
As for the prop problem. There are several. One is that by looking through a rotating prop things like e.g. clouds can't be seen. Though this is not very nice, you can live with it. I have not yet found a cure for this.
The other issue happening with prop is that you see kind of a massive disk instead of the blurr you would expect from a prop. This you can fix either by editing the prop texture and work the alpha channel or you can just replace the whole prop texture with one from another aircraft where it works correctly.
The
Shockwave Forum has many good threads about how to fix these issues. They are very supportive to help their customers to get their products running with FSX.
Edited: I just have seen your other question regarding the prop. Looks like you have a problem with a specific aircraft. Which one is it?
Cheers,
Martin