The explosions in Freespace are animation files that are played when things go boom or take a hit. I think there are four or five different kinds of them, two for normal fighter/capship explosions, the rest for missile and beam hits. You can replace these animations if you like, but adding more would propably require code changes and would be waste of memory anyway IMO. Not sure if you can increase the amount of particles spewed, but I doubt it would look that great.
Anyway, to get you started, grab at least vpview and aniview from this link:
http://www.descent-network.com/descman/Vpview allows you to view and extract the data from the vp files in your main FS2 directory. Aniview plays the ani files which Freespace uses for all animations, including explosions. If I remember right, explosions are stored inside sparky.vp in the effects folder, exp04.ani or somesuch. Hope this helps

Btw, you from scifi-meshes? Glad you found you way here
