Ok, listen up Cobra. Listen very carefully, i´ll shall say this only once:
There are 2 kinds of subobjects in FS.
The physical ones, where an actuall object is used.
And the coded ones, where a spot in a mesh is used by FS to point a subsystem. Like a fighterbay.
The latter one is made in PCS and ModelView, by choosing certain coordenates of the model and assigning the proper code in the table entry. Check around. The method is exactlly the same as turrets, basically.
As for physical subobjects:
First of all, you´ll need a TS plugin, called TrueView. Get it on the site Karajorma pointed out above.
Next is to remember a fundamental rule of modeling: organize yourself. Picture what you´re going to do first, BEFORE starting the work. It´s very hard to break down a mesh into seperate objects, once you´ve done it. So build them in seperate. If you want a certain part of a ship to rotate, for example, you must build it in seperate.
Once you have two objects, wich we will call the "main hull" and "subobjects", you need to group them. Basically, grouping them means adding a light to each object. It´s very easy to do.
Open Trueview (while on TS), and select your object. Then place a light next to it, and use the various viewports in TS to center the light with the object. Then move to TrueView, select the light (if you haven´t already) and drag in into the object in question. It´s just like Windows Explorer. It´s a drag and drop operation, all done in the TrueView window. You will notice that once you drop a light into an object, a small "+" sign will appear left of the object. That means it´s a "group". Open it by clicking on the "+", and you´ll see the object and the light.
Do the same for the object you wish to have as "subobject". Then, to complete the operation, you drag the subobject group into your "main hull" group (always in Trueview).
And that´s it. Name the groups acordingly, call the main grup "Freespace Model". Save it, and convert it.The rest is just like turreting, of wich you can read an extensive tutorial in Karajorma´s sig, as i had said earlier. You can also open a model from FS and check the hierarchy of it on TrueView, to get a better idea.
That´s it. Remember to organize yourself, and think ahead. Always.