You sure can use a PIR sensor with the v4. It uses a digital port (with regulator if needed). Here's a quick script example...

# Assuming PIR is connected to port D0
:start
If(getDigital(D0)=1)
Print ("On")
Elseif(getDigital(D0)=0)
Print("Off")
Sleep (2000)
Goto(start)
Endif

This is a very basic script, so you may want to add "Repeat" commands in to your script. Here is the link to a thread I started asking the same question, and a short video demo. :)

Thanks, Just what I needed. :)