I'm using the latest version of Directory Opus on Windows 7 64bit. I downloaded the button script for Beyond Compare, which is an OSP file. To install the button, I went to Settings/Preferences/Toolbars/Scripts and imported it. I appears in the list now and there's a check mark next to it, which I think means it should be active, but even after restarting the computer, the button doesn't appear in my toolbar. Does anyone know what I might be missing? Thank you for your help!
Installing the script makes a new command available, but won't add it to your toolbars. (It doesn't know where you want it, or how you want to use the command.)
If you go to Settings > Customize Toolbars > Commands, and look under Script Commands, you should find a Compare button which you can drag to your toolbar:
(Assuming it's the same script add-in that I'm thinking of.)
Wow, Leo, your fast! 
Yes, it is the same script add in. Thank you so much for your help!