I need to create a function that will identify and compile data for specific
24 hour periods. (In Excel 2003)
It may be a two step process but if there is some way to get it all done
with one function i am happy to hear it.

Data is in two columns, Reading Time (over a 24hr clock, for every day in a
month) and Raw Readings (which are running totals, not separate quantities).
Readings are not in uniform increments from hour to hour. See sample data
below:

Reading Time Raw Reading
7/31/2008 23:57 583200
7/31/2008 23:27 582875
7/31/2008 23:10 582833
7/31/2008 22:37 582766
7/31/2008 22:05 582707
7/31/2008 21:32 582642
7/31/2008 21:15 582641
7/31/2008 20:58 582641
7/31/2008 20:41 582640
7/31/2008 20:24 582639
7/31/2008 20:06 582639
7/31/2008 19:49 582638
7/31/2008 19:32 582637
7/31/2008 19:15 582637
7/31/2008 18:58 582636

I need to create a sum of raw data quantities per hour, per day over the 1
month period for trending purposes that looks much like the compiled data
below:

Reading Time Hour Quantity
9/1/2006 1:00 1 0
9/1/2006 2:00 2 0
9/1/2006 3:00 3 325
9/1/2006 4:00 4 305
9/1/2006 5:00 5 375
9/1/2006 6:00 6 272
9/1/2006 7:00 7 43
9/1/2006 8:00 8 0
9/1/2006 9:00 9 0
9/1/2006 10:00 10 0
9/1/2006 11:00 11 0
9/1/2006 12:00 12 0
9/1/2006 13:00 13 0
9/1/2006 14:00 14 0
9/1/2006 15:00 15 0
9/1/2006 16:00 16 0
9/1/2006 17:00 17 0
9/1/2006 18:00 18 0
9/1/2006 19:00 19 0
9/1/2006 20:00 20 0
9/1/2006 21:00 21 354
9/1/2006 22:00 22 307
9/1/2006 23:00 23 235
9/2/2006 0:00 24 148

Any suggestions? do i need to go into more detail?