In a few days, my 12" PB will be arriving. I plan to hook it up to my 21" monitor while using it at home. I plan to use both the built-in display and the monitor simultaneously. How will this affect graphics performance. Will each screen recieve half of the 32 MB of VRAM? So will everything be slow? I plan on running the monitor at 1600x1200, would it be better to just run it lid-closed with one screen?