Legacy.1 Rename this file to "Legacy.z01"
Legacy.2 Rename this file to "Legacy.z02"
Then use WinZIP to unzip them. They are multiple volumes but WinZIP should know that as it ZIPped them in the first place!
These archives contain the .WAD file + Doom Legacy files, just unzip them into a directory such as Legacy or something and you are ready to go!
Run DM Launcher to activate! Have 32-player fun!