Please help: conditional formatting based on two cell values!

Hi

I have done this before but seem unable to get it right this time:

I have a invoice spreadsheet and want to conditionally format cells in the 'due date' column to show when an invoice hasn't been paid on time.

On the spreadsheet:

Column A = DUE DATE
Column B = numerical amount if paid, or 'np' if not paid.

How do I conditional format column A to highlight cells if today's date is greater than the date in cell A and there is 'np' in cell B??

Any help would be great. This is really niggling me and I know I will feel silly when I hear the answer but my mind is BLANK!!

Thanks

This is highlighting some cells, but not the right ones!! I'm sop confused - I an't even work out WHY it is highlighting the ones it is!!