depends on which intel integrated graphics you have.
it was 11mb on the earlier ones like the i810. the newer ones use "up to" a certain amount depending on how much system ram you have. I think its something like 128mb max if you have 512mb or more, etc.
I dont think you can actaully set how much to use, unless its in the intel driver somewhere, but it is a variable size, so if it isnt using it, it will give it back supposely.
on linux / mac os its 11mb though i believe.