Passing an Argument into User Defined Command that's a VBSCript

Greetings Gurus, how do you pass your own arbitrary arguments into a VBScript in a user defined command (as you can with standard commands using the templates and &arg&).

For simplicity I have UDC with one vbscript line: msgbox(&arg&).!Documents/Scripting/Adding_a_new_Internal_Command.htm

Thanks Leo, that's what I needed.