The PV-143 is a 4 port card that shares one BT878 chip.  The bttv kernel module will load /dev/video0 automatically.  However unless your application supports accessing sub channels you will need to use the 'v4l-ctl' command to switch inputs on /dev/video0

This command below will make Port 2 on the PV-143 the 'active' port on /dev/video0

v4l2-ctl -d /dev/video0 -i 1

Replace the ending digit to access channels 2 and 3.  Switch this integer back to 0 to access Port 1