Using some decent software on the image from the IP camera
makes a hell of a lot more sense than farting around with a
separate PIR and sticky tape, ****wit.

I use this with my IP cameras:
http://www.pysoft.com/ActiveWebCamMainpage.htm

It runs on a low spec Atom based PC, and can be configured to email /
ftp video or photos as required when it detects movement in the areas
you specify.