IF statement using multiple variables to give multiple outcomes

Hi Guys,

Hope I've done this right as this is my first post.

I'm looking to work out an IF statement based on a series of dates entered to give 1 of 3 possable outcomes.

Where:
A1: todays date (exmaple =NOW())
B1: due date (exmaple 10/02/09)
C1: completion date (example 12/02/09)
D1: status (overdue, outstanding or completed)

D1: =IF(A1>B1,"overdue",IF(A1<B1,"outstanding",IF(C1<=>A1 & B1,"completed")))

I know the last part is totally wrong (symbols arranged in that manner), but to clarify i would like the date entered in C1 to override the other statements in the fomula to make it read "completed". If no date is entered in C1 then the formula will return either "overdue" or "outstanding" depending on the other dates in A1 and B1.

Hope this all makes sense.

Thanks for your efforts in advance.

Stuart