Okay, I'm lost.. I downloaded the file and saved it to Fallout 3. I went to Fomm and clicked Add New but couldn't find the file in Fallout 3.. I have no idea about esp/esm and there's no file named fomod.
First, have you understood what has been said about modifying anything installed to the Program Files folder? The gist of it is that you can't do so, not reliably, and not with mods.
If you didn't specify a folder when you installed the game, it installed to Program Files, and now you have fallen into Microsoft's Program Files Virtualization trap. In short, you cannot successfully write other files into Fallout 3's folder, so you cannot install mods.
What's worse, applications (like WinRAR) that do write into that folder appear to succeed, but they
actually write into a virtual folder that isn't that folder at all.
Other applications that don't know about this obscure "feature" of Vista and Windows 7 cannot find the files, so they do not show up in FOMM or in the game.
If you want too much detail, you can read a good explanation at http://www.hanselman.com/blog/VistasShowCompatibilityFilesAndTheScrumptiousWonderThatIsFileVirtualization.aspx
If you do not want endless trouble with the game, you should:
1. Uninstall.
2. Reinstall. When asked to specify the install location, do not give a location under Programs or Program Files. Give a location like C:\Bethesda\Fallout3.
3. Install mods to the proper folders under your actual install location.