1) Uninstall everything. Literally everything: FL itself, Discovery, FLMM. Back up any save games you want to keep first in a folder that is well and truly clear of any possible locations for Freelancer or mod installations.
2) Make a new installation of vanilla Freelancer - preferably from the original disk. Do not modify this install at any time, ever - it is your "clean" install.
3) Download and run the Discovery v4.88 installer. When it asks for your Freelancer directory, put in the directory of your vanilla installation that you just made. Then, make sure your desired Discovery v4.88 directory is in a separate folder to that vanilla install.
4) If that worked properly, you should be able to run Discovery. Test by attempting to join the official server. If it didn't work, do not proceed, and seek additional help.
5) To install older versions of the Discovery mod: If they have an installer (.exe), use the same procedure as above, but you won't need to install vanilla FL again.
Right...so...
I have installed Freelancer...AGAIN.
I have downloaded FLMM
I have found and downloaded the 4.88 Discovery file (from moddb?)
I select my freelancer game as the directory from which to install, and I tell it to install to a different folder.
As the programme is running, it says "copy failed" on EVERY file it wants to access, and then moves on to try to install, and flags each failure AGAIN with a box that I have to click "try again" "ignore" or "cancel".
It will NOT install for some reason.
Is the download simply a PATCH/UPDATE...or is it the full Discovery mod?
If its a patch/update, it obviously wouldn't find the required files since they wouldn't be there...?