2 HD cameras on a new Macbook Pro 15 inch?


So will I be able to run a Powerpoint input from VGA2USB and 2 HD video input on a brand new Macbook Pro 15 inch with SD harddisk, maximum RAM and CPU and so on? Do I need to get a 17 inch for the express slot or can I connect an exra camera some other way?

And will it lag?

Thank you!