I don't know what .exe file to run to play Noctis IV CE! Although there are a lot of .exe files in the main Noctis IV CE folder, most of them do exactly the same, but differ in the way they accomplish it. Old Go!.exe, for example, launches the main Noctis IV CE program directly, and is therefore least likely to work properly on your system. Normal Go!.exe and Alternate Go!.exe both apply some forms of optimizations to the main Noctis IV CE program, and it is therefore recommended that you run either one of these two launchers, unless Old go!.exe works perfectly for you.
There might also be a few other .exe files in your main Noctis IV CE folder, such as WNoctis.exe and DWNoctis.exe. These contain the Windows 'port' of Noctis IV CE. Note however that the Windows port is less feature complete and might be buggier than the DOS (standard) version of Noctis IV CE. Unless you want to view the Debug console (which you probably don't want), run WNoctis.exe, otherwise run DWnoctis.exe (the 'D' stands for 'Debug')
Another .exe file you might encounter is HacIRC.exe. This is an IRC chat 'wrapper' using the Xnice system for Noctis IV CE, allowing you to chat whilst inside Noctis. HacIRC is by default setup so that you will connect to the 'official' Noctis Internet Relay Chat channel. For more information about the IRC network in general, please consult Wikipedia. For more information about the Noctis IV CE IRC chat channel, please browse the AnywhereBB forums. Need help with HacIRC? Read the official HacIRC readme (if existing) or ask on the AnywhereBB forums.