Sorry I have to point this out, it's bugging me. you're thinking of dedicated and Shared memory for the video card.
Virtual Memory is using the HDD as system memory.
Shared memory isn't very effective as it has a much slower bus speed than the memory typically used for graphics cards. It also steals from system memory. 99% of the time more than 128MB shared will do nothing for you.
Besides that, anything requiring more than 128MB of video memory will typically be too hard for the processing speed of that Graphics chip anyways.