I took a screenshot so that you can see the differences...
First Computer: VLC 0.8.5 (if I remember) with windows xp:

Second Computer: VLC 0.8.6h with windows vista:

So the first computer has a better image quality than the second.
Now you can see the differences with this GIF:

I tried to compare every setting but I didn't manage to solve the problem...
Does someone know how to have the same quality ?