This seems to be a laptop computer:
"Mobile Intel(R) 915GM/GMS,910GML Express"
Display Adapter 1: LCD screen
Display Adapter 2: External monitor port
Monitor 1: LCD screen
Monitor 2: External monitor port
Monitor 3: A possible Docking Station or S-Video/Composite port
Monitor 3 could be explained through the presence of extra video ports on
your laptop; Standard VGA is a blue or black 15-pin connector, S-Video is
a round shaped connector which may be proprietary multi-pin (4, 5, 8,
etc.), Composite is a round 1-pin connector, docking station port is
rectangular of shape and is located at the bottom of your laptop in most
cases.
You have not stated any problems with these two adapters and three
monitors, therefore I will assume your system is working fine and you are
merely wondering about the presence of the 'duplicates'.
This is normal for a laptop computer, each 'device' stems from one piece
of hardware and it's software: your graphics card and it's drivers.
