If anyone is interested (not to hijack the thread), but I have two of these (Overhead Door Sensor) that need a home (I no longer need them)... $20 for the pair. Just PM me if you're interested.They are magnetic contacts just like you would have for an entry door.
There are special garage contacts made for roll up doors.
http://www.discounthomeautomation.com/cgi-bin/dha.pl?pgm=co_disp&func=displ&retail_id=30&product_id=7981&session_id=0,0&search_id=810510
The door contacts can tell you the status of the door, whereas motion sensors can only tell you if there is motion in the garage.
Here are several ideas on this as well.I already have Homeseer Pro for the backend, and I built a dedicated PC to run it, so that is covered. I like the magnetic option, where it knows if it is open or closed, that is huge to me for what I want to do. I'll do some research on those as that will more than likely be the approach I take, thanks!
jmark, email me, as i will take them if you still have them.
Jon