I could be completey off base here, so someone correct me if I am wrong <_<
I think most hardwired PIRs are going to have a contact that is either open or closed. So you would need to attach those contact wires to some sensor that can determine if the loop is open or closed. Perhaps the computer can do that itself, or it might take some box that is attached to the computer.
Wireless PIRs are going to send a signal that is made up of at least two parts, an address and status. You would need a wireless receiver to pick up on those signals that is compatible with the PIR.
I know there are several manufactures of wireless PIRs and they are not usually compatible. So a X10 wireless PIR needs an x10 receiver, a CADDEX wireless PIR needs a CADDEX receiver, etc, etc, etc.
From a homebrewed angle, I think the X10 wireless PIR might be a good start. You can use a
WGL W800 receiver to capture those codes so the computer can act on them. All you have to do is write your own code to act on those commands. (Of course there is already software out there that does that, but you could integrate this into your own system pretty easily). WGL even has released the
W800 protocol document so that information is all at your fingertips.