Ok.. There are a few options..
Option 1: open rm2k3, open your project. Copy all of your maps, then open the battle system and paste them all. You will then need to go to your project directory and copy all of the files (any gfx of course) and paste them in the battle system's directory but do NOT overwrite any of the files.. And lastly if you have any common events/etc (anything that's in the database folder like animations) then copy them all and put them in the battle system. Don't overwrite anything of the battle system. You will however lose all of the variable names from yor project.. To get them back you just open your old project and look at the variable names.. Then write them down and go back to your new game and re-name them. -This is the preferred method because then you don't have problems occuring when you did something to the battle system while transferring it.
Option 2: open rm2k3, open the battle sys project. Copy all of the maps, then open the your project and paste them all. You will then need to go to the battle sys project directory and copy all of the files (any gfx of course) and paste them in the your project's directory.. And lastly with common events/etc (anything that's in the database folder like animations) then copy them all and put them in the your project. You will however lose all of the variable names from the battle system.. To get them back you just open the battle sys and look at the variable names.. Then write them down and go back to your game and re-name them.
I really don't want to say that again..