At the moment @script only works with Rename. You can't use it on its own.
You have to either use this technique or put the script in a file and call that from Opus as if it was an external program.
Is AutoIT a language or does it expose some scriptable objects (like AutoItX3.Control) to other languages like VBScript? What you've written looks like VBScript and if so then you're doing it wrong. Have a look at one of my example VBScript Rename functions to see how they create and use the Shell and Filesystem objects.