Excel 2007 : Identify unique employees, and employees with a change in hours

I need to ffind a way to show the following, I have a list of employees with their assigned hours. I want to compare two months, I need to know a) if there are any unique employees, ie employee only shows up in one of the months, and b) if the employee shows up in both months compare their hours and flag/mark if the hours are not the same in both months.