I used to have a nice tutorial on that...  Lep where did they go?

Ok, first question, do you want your lasers to move or not?

If they do not move, you will need 3 entities.  1 env_beam, and 2 info_targets.  Place the info_targets 1 where the laser starts, the other where the laser ends.  Place the env_beam whereever.  In the info_target propreties, give them a name.  Not the same name, something like lassta and lasend.  In the env_beam propreties, you can give it a name if you want it to be triggered, if not leave it blank.  In the start entity and end entity values, put in the names of your info_targets.  Put a life value of 0 seconds that way it will always be on.  Tick the "start on" flag.  Compile, and you will have a working laser.

You could also just use one env_laser and one info_target.  Really don't need 2 info_targets.  Just have the env_laser be at the point where ya want the laser to start instead of being anywhere and having to use 2 info_targets.

Gets the same effect..with one less entity.