On another post you said the zip ask for a password, here you said that happens when downloading missions.
I am not sure which one is, but I can tell you that I don't remember any mission to ask any kind of password when downloaded or unzipped.
On the post you find the problem (Feda's Ixian campaign) that file got "corrupted" when the forum changed, so the file you may download from there it's broken and can't be unzipped in any way; did you try to download any other missions?.
If you want to try other missions, or just this one but being sure that the file it's working fine, check this link. https://forum.dune2k.com/topic/27756-all-completed-mods-and-tools-index-dune-2000/
The Feda's Ixian campaign it's grouped with more campaigns, but feel free to try any campaign you want; all post and files should work fine and no password it's required.