First of all download the new weapon pack and read the instructions carefuly. Usualy you need to go to My Computer/Local Disk/Program File/Microsoft Games/Combat Flight Simulator 2/SCENEDB/weapons/there you are going to find two Folders. One call scenery and another one call texture.
Paste the BGL and BMP in there appropiate folders scenery and texure folders. Inside the scenery Folder there is a file call filelist Dat file. Delete it.
Go back to the Airplane or group of planes you want to add with the New weapons. We are going to use the the A6M2 zero as a example. Open My Computer/Local Disk/Program/Microsoft Games/Combat Flight Simulator 2/AIRCRAFT/ A6M2_ZERO. Open the A6M2 Folder and there should bee Six Folders and four files call a6m2_zero Airfile,a6m2_zero DP file,aircraft CFG file,a6m2_zero CDP file. Delete the CDP file and that should do it.
Do not worry about deleting this files. They will be replicated by the CFS2 program. This files only record the setting of their respective Folder to keep the program stable. Once you delete them they will be replace with new ones with the new recorded information.
Now you can go on a Happy Bombing Mission!