If you're using the media vp labelled 3.5.6 (a or b) you'll need to have the -t32 command line tag enabled, otherwise FS won't recognize the 32bit files and thus not load any nebulae, primary weapon shots, or warmup glow for beam cannons. The problem is that AFAIK, not every build will recognize the -t32 tag. Bob's _t and the latest build (the one without any letter extension) will recognize it, but I don't know about any of the others. Also, if you chose the _t build, you must use -htl otherwise it'll crash as soon as you either enter the techroom or commit to a mission.
Later!