Things you'll need

How to add beam turrets

Glue a light (local light) in Truespace to the object you want to be a beam turret to as sibling. The glue the light/object combo to the hull as child. Save the the entire model as a COB. Convert the COB using COB2FS2 or COB2POF. Open the POF in Model View. Click on the subobjects tab to find out what subobject your turret is. Open the POF in FSMM2. Click on the objects tab. In the pop down list select the subobject your turret is. Then in the properties box put the following properties.

$special=subsystem
$fov=40
$name=turret

That defines where is is viewable (I belive) and the name of the targetable data that will be used in Freespace2. Then in the model name unter "turret01" without the "s. Then click on the gun turret tab. Click add turret. Select in the Object Parent Number and Physical SOBJ Parent the name of your turret in both.(if you followed correctly it should be turret01) In the normal vector you need to define where your beam will fire. Enter these numbers for which way you want the beam to fire. Remember the commas in thses numbers define the seperators between the X Y Z in Normal Vector.

1,0,0 fires right
-1,0,0 fires left
0,1,0 fires up
0,-1,0 fires down
0,0,1 fires foward
0,0,-1 fires backward

After that add a firing point. Now extract the ships.tbl using VPView. Find a ship you want to replace with your ship. Change the name and the pof file to refer to your pof file. Enter this to refer to your turret in the subsytems area of the ship.

$Subsystem: turret01,20,1.0
$Default PBanks: ( "BFgreen" )

BFgreen is the largest terran beam, you may want to change that.