not a problem man.
just go an buy a webcam if you dont already have one built into ya puter wit the motion sensor option. mine came like this.
but look on the net google on the specs of said cams that interest you an chek details an capabilities. almost all newer puters manufactured wit cams built in have this opstion within the webcam manager software. just another option along side ya capture modes etc..
and you can set them up to send you an email everytime it goes off. and if you have a data phone like a blackberry you can arrange your emails to be sent to your phone as well. and when ya email is sent a "hey you got a capture on ya cam" type message it send along wit it a file containing the video it captured or even a link to it where its stored on a database somehwere and just on ya cell follow the link and VIOLA!!!
doe sthat help any? if not let me know.
edit: PS. also you of course gotta leave ya puter on whle this happens (when you leave ) inorder to work.
and wat it does it when ever it senses motion in the room in the viewing field of the camera it startes recording and stops whenevr you set it up for. say like settin it up to stop recording ten seconds after movement stops, 20 30 40 seconds.... etc... you can do the settings how you like