Summing values from different dates for monthly total

[HP RodNuclear]

I attached a dummy file to explain what I am trying to do but in the file called emergent, I have dates associated with dept names (ops, rxs) and numerical values associate with those dates and those departments. On the 2nd sheet named 3 month estimates, the emergent column (Columns D, H, and L) sums up the values from the emergent sheet for each department from the last 3 months. So for example, as you can see from the spreadsheets, from the month of October, Ops had a TOTAL of .008 (.005 on 10/5/2010 and .003 on 10/22/2010).
What I would like to do is on the 3 month estimates sheet is to make the emergent column more automated--meaning, by use of a formula or macro, it automatically will look for values associated with the current month listed in row 1. However, I don't know how to do this b/c the emergent values are day by day listings, and the 3 month average is on a monthly basis and I don't know a formula for vlookup to know to stay within the certain month's ranges from the emergent spreadsheet.
If any of this is unclear, basically just think of it this way: I want the emergent values from each department in the 3 month estimates sheet to be the sum of the values from the emergent spreadsheet from the respective departments WITHIN that particular month, which in this case would be the values from October, November and December 2010.

Thanks.