The Widescreen mod is packaged and installed with WeiDU and is distributed as a self-extracting archive. To install, simply double-click the archive and follow the instructions on screen.
Alternatively the files can be extracted from the archive using WinRAR. If properly extracted, you should have a widescreen folder and setup-widescreen.exe in your game folder. To install, simply double-click setup-widescreen.exe and follow the instructions on screen.
Please run setup-widescreen.exe in your game folder to reinstall, uninstall or otherwise change settings.