Panama Red got there before me...JSGME is a super program.
Aim the installation of JSGME at the root folder (i.e "CFSWW1 Over Flanders Fields").
Run the program (that will set up the Mods folder and get it ready) and then close it.
Extract the downloaded zip file into the Mods folder - it will create a folder "HPWFB1_0" with subfolder "Aircraft")
Open JSGME again.
The box "Available" will show the mod.
Move it across to Activated by highlighting and then ">"
Good to go.
To remove it, use the "<" button. OFF will restored to vanilla.
At least, that is the theory, I'm just doing it now!
Just a super bit of software. I use it for all modded games.