I build systems for friends all the time. I recently build a pretty nice hacknslash version you might be interested in. Total cost $1000. Its very very simple. 4 acer netbook/laptops, using the built in webcams as security cams. It seems foolish but is actually quite neat. They all run yawcam ( free software ). All cams can be checked via cellphone or web , all have motion detecting or reverse motion detection, snaps are sent via txt message when an alert is triggered, snaps are also logged to ftp, motion detection can trigger any exe you want so possibilities are pretty endless, use this
http://www.productwiki.com/usb-power-bar/ to do things such as start floodlights when acticty is triggered