Just reading your post and had the same question. Looking in the manual on the disk that came with my camera the differences are below. Still learning myself.
6.6.1 Configuring Motion Detection
Purpose:
Motion detection detects the moving objects in the configured surveillance area, and
triggers the certain action as a respond to detection.
In order to detect the moving objects accurately and reduce the false alarm rate,
normal configuration and expert configuration are selectable for different motion
detection environment.
6.6.8 Configuring Intrusion Detection
Intrusion detection can set an area in the surveillance scene and once the area is been
entered, a set of alarm action is triggered.
Steps:
1. Check the Enable Intrusion Detection checkbox.
2. Click Draw Area, and then draw a rectangle on the image as a defense region.
Note: when you draw the rectangle, all lines should connect end to end to each
other. Up to four areas are supported.
You can click Clear to clear the areas you drawn.
The defense region parameters can be set separately.
3. Choose the region to be configured.
Threshold: Range [0-10s], the threshold for the time of the object
loitering in the region. If you set the value as 0, alarm is triggered
immediately after the object entering the region.
Sensitivity: Range [1-100]. The value of the sensitivity defines the size of
the object which can trigger the alarm, when the sensitivity is high, a very
small object can trigger the alarm.
Percentage: Range [1-100]. Percentage defines the ratio of the in-region
part of the object which can trigger the alarm. For example, when you set
the percentage as 50%, half of the object entering the region will trigger
the alarm.
Arming Schedule is configured to set the time you want the function to be
enabled.
1. Click Edit to set the arming schedule.
2. Choose to trigger alarm actions as Notify Surveillance Center, Send Email,
Upload to FTP and Trigger Channel or trigger the Alarm Output.
3. Click Save to save the settings.