Apple has made available documentation to aid you in adding AppleScript support to your own custom applications. This documentation can be found here.
In addition, the MoreOSL C library helps carbon developers to implement scriptability in their applications.
You can allways find lots of help at Apple’s applescript-implementors mailing list and its archives.
Extra tools, source code and reference material here:
Don BriggÃ¢â?¬â?¢s Suite Modeler and sample scriptable cocoa applications.
The GraphicKit, by John HÃ?¶rnkvist, a powerful sample scriptable framework.
Andrew Stone (author of Stone Studio), also wrote an article about Ã¢â?¬Å?Adding AppleScript Support to Cocoa AppsÃ¢â?¬ at MacTech.