You can download adom-111-elf.tar.gz (ADOM 1.1.1 for Linux) from the ADOM website.
You'll need a program that can handle tar.gz files to uncompress the downloaded file. WinZip (http://www.winzip.com/) can handle tar.gz files and is easy to use.
When downloading adom-111-elf.tar.gz, some browsers may rename the file on download, preventing WinZip from opening it and decompressing it properly. If this happens, save the file to disk, rename it to its proper name, then open it in WinZip.
Upon opening adom-111-elf.tar.gz in WinZip, WinZip will ask you if you want to decompress it to a temporary folder and open it. Say yes. Next extract the contents to the ADOM Sage directory. If you already have the DOS version of ADOM, then the only file that you really need to extract is "adom"; the other files are just documentation.