Although I've never tried this myself, there are two exposed functions off the Global Vegas object that claim to be able to run another script
// Run a script from a file. Parameters: scriptFile: the complete file path of the script to run
void RunScriptFile ( String scriptFile )
// Run a script from a file. Parameters: scriptFile: the complete file path of the script to run scriptArgs: script arguments
void RunScriptFile ( String scriptFile, String scriptArgs )
Gary, that command will work to run a script but only from within a Custom Command.
From the scripting API list for Vegas Pro 8:
"Custom commands can run scripts using RunScriptFile and RunScriptText methods of the Vegas object. These methods will fail if called from within a script."