Welcome !
I'll save you some time
1.) don't put anything in the Freespace 2 data folder.
2.) make a folder called mediavps and put the media vp files in there. I suggest using the latest CVS build and the 3.6.8 Delta Mediavps on this site.
3.) if you have to add stuff that wants to go in the "freespace2 data folder" it goes in a folder called data in the mediavps folder. anything that is in this data folder overrides whats in the mediavps. Most all shine, glow maps are in the mediavps already, except for a few newer things that you don't have to worry about until you become more familiar with how the media vps work. In fact, you don't even need this data folder at all, but if you want to add something thats not in the mediavps or that overrides what's in them (like table files, models, etc.) they go in this data folder, in a certain order.
4.) Get a program (like vpmage) that can read vp files and look inside of them to see how they're structured. that's the structure you should follow for the data folder that is in the mediavps folder you've made. 95 percent of the time, it's already in the mediavps (at least, with the 3.6.8 mediavps)
5.) To use the mediavps, you should load them as a mod. you don't have to do this, but it's the preferred way to do it without causing problems when you have multiple campaigns (mods) later on.
6.) When you install a new campaign (mod) you should make sure it has a mod.ini file that points to the mediavps folder in the "secondrylist" setting. that way you choose the mod directory in the launcher, and it will load the mod and the mediavps as well. This is the multimod system. It's a little bit harder for newbies to use the SCP this way, but it's a HELL of

better if you end up installing a bunch of (mostly older) mods. See DerelictSCP for an example of how the mod.ini should look.
Understanding all the above will help you out a great deal and cause you less trouble with overlapping table files and older mods in the future. You'll figure it all out with a little patience, I did.