I'm fairly familiar with these matters, and I do occasionally feel guilty for lurking and not contributing. Either I, or individuals I can find at SDnet, would probably be able to help with charts and formulas without any more flamewar threads than absolutely necessary. And some simply are inevitable with a project like this.
As to the question of what joules and watts and tons mean in terms of damage, well that's a fun one. For example, consider a nice spherical nickel-iron asteroid ten meters in diameter. You want to vaporize this asteroid; the absolute minimum energy required is the equivalent of 7.5 kilotons of TNT. A kiloton is 4.2 terajoules, that is, 4.2*10^12 joules.
However, a sci-fi weapon rated at 7.5 kT is far more likely to crater or melt this asteroid than it is to vaporize it. Why? Well, vaporization is what you get if you put a 7.5 kT nuke inside the asteroid and set it off. That's all of the energy applied evenly to the asteroid far faster than it can be reradiated. You detinate that nuke at the surface, and less than half the energy is going to go into the asteroid, and not at all evenly. Now you try hitting the asteroid with a high-wattage laser pulse rated at 7.5 kT. Some of the laser will be reflected, depending upon what sort of laser it is and what the surface of the asteroid is like. The initial hit will hit with full power, but now you've got vaporized and melted metal streaming out of the hole and diffracting the laser. Furthermore, you're only hitting a tiny point on the asteroid, so there's more of a tendency for the laser to put a hole in it than there is for the whole thing to instantly turn to gas.
Even so, it really shouldn't be that hard to come up with nice little values called 'damage points' if we put our minds to it. However, I know little about how damage and such are calculated in FS, and what sort of little bits of programming it would be possible to squeeze out of the local CS types, nor do I have any idea what might have been determined to be the current state of FS tech, so I really don't know where to begin.