You mean the overhead where you jam guns and missiles in your ship? Couldn't be simpler. First use VPView to crack open sparky.VP (or the hi-res version if you prefer). Then extract, say, loadfighter06.pcx (or 2_loadblahblah for the hi-res version).
In Modelview, line up your ship overhead and hit print screen. Open your graphics editor (Paint will do the job fine) and hit paste, and the screen shot should appear from your clipboard. Then simply cut out your ship's piccy and paste it over the Volition one in the loadout image you extratced. Done. Oh, and make sure you give it the right number of loadout slots. Like the Herc would have two gun and two missile slots, whereas the Myrmidon would have two and three respectivly.
Now look in your ships table - there is a line for specifying a loadout image. It's near the bottonm of the netry, but before the trail info and looks like this: $Ship_overhead: Simply specify the name of your overhead file. Make sure the file is an 8-bit PCX and named properly, then slap it in your Interface folder. Job's a good'n
