What Myke is telling you is to put this line
?! (local server): exit
at the top of your cutscene script.
so when the cutscene starts, your pc & the other will do a check (on the cutscenescript...) to see whether it's the local server or not.
If it isn't (? !(local server):exit) it will not execute the rest of the cutscene on that pc, giving you controls back so you can be a player in the cutscene the other one has on it's pc... eh that was a long breath ;D
for example your cutscene could start like this:
?! (local server): exit
enableRadio false
_camera = "camera" camCreate [-78104.63,-13727.56,50157.81]
_camera cameraEffect ["internal","back"]
;=== 12:47:04
_camera camSetTarget [-78104.63,-13727.56,50157.81]
_camera camSetPos [4872.84,10876.24,42.19]
_camera camSetFOV 0.700
_camera camCommit 0
@camCommitted _camera
....
....