Playing your PS2 through a computer capture card will always introduce lag that makes all games unplayable. Your only alternative is to buy a hardware device that is meant for console playback. Capture cards are not the answer. Next time do some research.
you want to use a cheap card that uses wdm drivers (no encoder)
you could run external task(wintv or what ever program comes with the cheap card) with the card that would mean you could start from within gbpvr
but unless you actually want to use gbpvr for its intendered purpose its a waste of time