If you calculate what the speed will be after applying the impulse, then you can compare the current speed with the calculated speed.
If either of these is true then apply the force:
[code]+calculated speed<max speed
+calculated speed>=max speed
+calculated speed<current speed[/code]
To calculate the speed take the same value used for applying impulse and do this:
calculated speed= distance(0,0,vx,vy)
I made my own capx to figure out a solution so here it is for a working example:http://dl.dropbox.com/u/5426011/examples16/spaceship.capx