You're doing it wrong.
Uhh, I don't think you need to download anything for the mission editor...
Correct, it comes with TGE. You need to create a batch file to open Mission Editor.
Or put -modeditor.
search mision editor in addons section.
Its not an add on.
yes it is.http://forum.blockland.us/index.php?topic=86817.0
Thats to make it easier to get it, it is an add on, but you can get mission editor without having an add on.
No dur. To make it easier! It's what I use.