Good advice as always from Hagar there.

The other thing you should keep a close eye out for is scenery add-ons that use Flatten and Exclude commands. These are always referred to in the download documentation if required.
In order for you to be able to add these, the scenery must have a separate entry in the scenery.cfg file. (Actually there is a way around this, but to keep things simple I won't refer to it now).
To achieve the separate entry, the scenery and texture folder (if present) of your add-on scenery must first go into it's own folder. e.g. You'd make a new folder calling it "My New scenerys name (whatever you like)" and drop the folders into it.
That folder can then go pretty much anywhere in your FS2002 directory. I usually put it in the Add-on scenery folder.
You'd then add it via the Scenery library "Add area" button. This has the effect of adding it to the bottom of the scenery.cfg file (as well as enabling it in FS2002 of course). Once there, you'd edit scenry.cfg with notepad, scroll to the bottom where you'll find the new entry, and add the flatten and exclude commands as detailed in the download.