A. Compile the script. B. Switch to the Project window. C. Select Customize from the Project menu. D. On the Customize dialog, select Layout under Type dropdown. E. Select Buttons under Category. F. Click the New button. G. Double-click the Click property in the Customize dialog box. H. Enter the name of the script in the Script Manager and click Select. I. Close the Customize dialog box.
For more information, see 'Customize dialog box' in ArcView Help.