You cannot change these values in Windows 7 or in Vista. Microsoft have decided that Windows can manage these parameters better than users can and so there are no user controls.
On most PCs these days, dedicated video memory is a physical RAM chip that is part of the graphics chipset and is impossible to change. Windows adds shared memory to this from available RAM, up to the maximum of 1755MB automatically when the running applications (like games) require more memory.
A few computers may allow you to set a maximum for this shared memory in the BIOS but probably all OEM Manufacturers do not allow such changes in the BIOS.
The only thing you can do now as a user is to make sure you always have sufficient free RAM by maxing out the RAM.
It has been some years now since you could change these values. Microsoft attributed a very significant number of computer crashes to users setting inappropriate values and so removed the facility.
i tired FIFA11 and CALL OF DUTY these two games to check my video card, it failed to change this Vmemory whatever memory was dedicated it is same after runing these two games (not simultaneously one after other)
more over i check this with other samsung laptop it is changing.
finally i have restored complete system still i am not able to get this
that link is related to virtual memory which means whenever your trying to open any application that will stores in this memory and then will run and Videomemory is something related to display like giving good graphical display to the application