ALerts for Customer Credit limits

Hi

Is there a way to set a warning for all customers which would display when they have approached their credit limits i.e something like a watch list but it would not be specific to a set amount as all customers have different credit limits. Would this be a custom program where we would have to write a custom application which would use some sort of an alert to let the user know when customer X is at their credit limit. We are not using Sales order processing as this would be much easier to manage. We are