<newbie in training>
I was browsing the general FS forums, and this topic caught my eye. I always liked the ability to glide in other games. SO quickly scan through the thread and try the first button that should do something... Q. Of course, that's for shields. So I try the second one: Shift-G. Nothing. So I read the thread carefully, and come to the conclusion, that I have absolutely no idea what's going on here. Too many abbreviations...
</newbie in training>
Basically then FS2_Open engine supports the feature but the Freespace 2 campaign does not. It was written before the Glide code was added and it would severely change the gameplay to add it to the main campaign now.
There are ways to add the feature to the campaign yourself using a .tbm file. There may even be a suitable one lurking around. The easiest way to try it out though is to download a mod or total conversion that supports the feature. Wing Commander Saga (from here on HLP) and Beyond The Red Line (Follow the link on the tool bar to Game-Warden) both have ships which can glide for instance.
btrl and i think even tbp use custom exes. how custom seems to be something their really not open to divulge it seems 
BtRL used a slightly altered version of 3.6.9 Official. The only reason for this was between January (when 3.6.9 was released) and April (When BtRL came out) there were several bugs fixed that needed to be fixed for BtRL to work correctly. All the fixes are in CVS now and we'll be going back to the 3.6.10 branch after it's released.
The only customisation in the launcher was a few different pieces of artwork and a change of where the URLs point to for the forum buttons.
TBP uses nothing more than the Inferno build of 3.6.9 Official as far as I know.