From the Vegas 6.0 Help menu (same for Vegas 7.0):
Running a script
From the Tools menu, choose Scripting.
Choose a script from the submenu or choose Run Script from the submenu to browse to the script file (.vb or .js) you want to run.
Adding scripts to the Scripting menu
When you start the program, Vegas software looks at the Script Menu folder in the Vegas program folder to determine which scripts appear in the Scripting submenu. This folder is c:\Program Files\Sony\Vegas 6.0\Script Menu by default.
Add or delete scripts in the Script Menu folder to change the contents of the submenu.
From the Tools menu, choose Scripting, and then choose Rescan Script Menu Folder to update the menu.