changing "invalid username or password" message - how to do?

Hi folks - I am in need of a way to get a message to non-paying customers when they try to login. Is it possible to change the "invalid username or password" message to read something else? Or, is it possible using radius to force a dial-in customer to redirect to one web page only (a non-payment notice page?) I can provide more info if needed. I am currently not using freeradius but will use it if this will work somehow. Thanks, AW