On Windows, the emulator executable is the hatari.exe.
There is no conventional installer you just need to unzip the Hatari zip file in a folder of your choice. You can download Hatari for your OS here. My choice here is Hatari, which works very well and it is available for Windows, Mac and Linux. There are a handful of Atari ST emulators, and some of them are really good and easy to use.
