This is not how it works. You really want to set that number as low as possible. By claiming 2GB or more, you hurt yourself in memory capacity for other tasks when not using the GPU in gaming etc, as it will not use this claimed volume for anything other than the GPU. The way Windows' memory Heuristics works is that it always selects the fastest memory pool available. Whenever your pooled VRAM runs out, it will go to whatever is left available, which is more system memory. It's only when you have too little system memory that you can sometimes see some benefit of increasing this number, as it will start fileswapping designated VRAM to the harddrive less significantly.
Just go into the BIOS and leave it at 256MB or something. More then plenty for Windows Desktop.