How do I track a change in field and log it?

I have a form where a customer needs to track a status change from a drop down.  When that person makes a status change, to record their name, and date and what the status was into  a log format.  What is the best direction on capturing this information.  It would have to either be appended to existing text or log like a repeating table.  Which ever is easiest.  Please help,