Sum/average a conditional sum

[Dude]

I have been looking through the forums searching for an example to a problem but can't find something that readily pertains.

I am using Excel 2003
I am looking for a sumif, sumproduct, sum(if( or whatever can interrogate 4 colums in a row and when all 4 columns fit the conditions perform a mathematical function on the value in the 4th column and sum the results for the entire table.
Ex.

Let
Column A = Purch or Fab
Column B = PO or SO
Column C = status (Late, early, on-time)
Column D = due date
________________________________A_____B____C________D_____
ex. I need for every row that has | Purch | PO | Late | 11/20/2010 | I need today()-D= 95

=IF(A=[true] AND B=[True] AND C=[True] AND D < Today() )

sum total # of days that all of the rows that evaluate to true are < today()
average total # of days that all of the rows that evaluate to true are < today()

I have been able to count the number of rows that meets the criteria but am unable to figure out how to then perform a mathematical function on 1 of the criteria and sum the results of the functions.

And, I can't add another column to do the sums that could then be totalled.
Perhaps I am over thinking it.
Help .......