I'm trying to download GECK for FONV, but the file I download is just a zipped folder with the geck application itself, and icon, a readme, and the file extension. I can't run the file because it's missing a .dll file, and when I looked at the FAQ, it said to re-install the file. Where can I get the actual installer?

FO3 Geck files were installed alright. Installer was gotten from what I'm assuming is the official page (geck.gamesas .com/index.php?title=Main_Page).

Do I need to manual install?

Those are all the files you need, but they need to be in folder where New Vegas has been installed.