The Daodan DLL patches Oni.exe to be able to run on modern machines, as well as adding new features and Flatline (multiplayer). The Daodan file is actually called "binkw32.dll", but is totally different from the binkw32.dll that comes with Oni. Drop this into the folder that contains Oni.exe, replacing the DLL that's there. See this page for more information: http://wiki.oni2.net/Daodan_DLL.