One way...
For all versions of Excel.
A1:A20 = dates
B1:B20 = values to sum
The best way to do this is to use 2 cells to hold the date boundaries.
D1 = start date = 1/25/2008
E1 = end date = 3/17/2008
Sum is inclusive of start and end dates.
=SUMIF(A1:A20,">="&D1,B1:B20)-SUMIF(A1:A20,">"&E1,B1:B20)
Or, you can hard code the dates:
=SUMIF(A1:A20,">="&DATE(2008,1,25),B1:B20)-SUMIF(A1:A20,">"&DATE(2008,3,17),B1:B20)
For Excel 2007.
=SUMIFS(B1:B20,A1:A20,">="&D1,A1:A20,"<="&E1)
=SUMIFS(B1:B20,A1:A20,">="&DATE(2008,1,25),A1:A20,"<="&DATE(2008,3,17))