First let me explain something, me and my players never quite understood how a Power Armor suit could do as much damage as a Mecha 10 times its size, so we sat down and hashed out some new rules for this situation. Here they are.
All Power armor and Hand held weapons do what I call K.D.C. or Kilo Damage Capacity.
All Mecha weapons do normal M.D.C.
All Spaceships do what I call G.D.C. or Giga Damage Capacity. This is the end all be all of damage.
Now the breakdown of this system:
10 KDC makes 1 MDC
100 MDC makes 1GDC
The reason for these increments is for ease of game play, a power armored person can still go up against a mecha and have a small chance to win, but he has to be smart. The increment for KDC to MDC is low that way a power armor can do damage to a mecha still. But it is unlikely that a mecha is going to do alot of damage to a spaceship that is the reason for such a high increment for MDC to GDC. All in all it is a very playable and logical system.
This system doesn't take much to integrate into a presently running game, and they make the game more enjoyable for players that aren't MUNCHKINS. The listed damage is still what is written except for the type of damage. (ie. a power armor rail gun listed as 1d4x10 MDC now would do 1d4x10 KDC or 1d4 MDC this makes power armor more to the place it was, I believe, meant for, shredding grunts, and all mecha damage remains unchanged. This also helps out if you are using my Mecha and Power Armor Construction Pages.
There are some exceptions to these rules, any lost tech weapons, high tech weapons or such stay as they are listed in the book. Also the gods out of the Pantheons book still do the listed damage they have. A DM may also make other exceptions as he sees fit.
NOTE: Yes I love computers that is were I got most of the ideal for this.
Here is my New Mech Damage Rules they are in a window wordpad form so just download them and unzip thenn double click on it.