Changes since then include additions to the interface and support for Macintosh DLLs. Nevertheless, much of the information on this page is still very useful.
Scripts call DLLs with the dll.call verb.
The pathToDLL parameter is a string or filespec specifying the location on disk of the DLL file. The procedureName parameter is a string specifying the exported procedure in the DLL that the script would like to call. This name is case sensitive. The param1, param2, etc. This document assumes you are familiar with writing DLLs.