Conditional Format based on Months.

Hi

In Column D of my work book are a list of months, I'm trying to use conditional formatting to do the following:

Highlight green the cells in Column D where the month is due (i.e the month is now).
Highlight orange the cells that are one month passed the due month.
Highlight red the cells that are two or more months passed the due month.

I'm having trouble working out how to accomplish this - Can any one advise what would be best.

I'm using Excel 2007.

Thank you.