Q: Find cell reference containing specific value from current position up

Hi.

I'm having some difficulties in defining my formula. I'm pretty sure that this should be possible.
I have a table containing values and dates. For each change in dates, I should summarize every value for that date. I cannot use the autosummarize function, because I do not want the sum to be beneath the values, rather in a column to the right of the values.

I have created a formula which checks for a change in date: =IF(C15=C16;0;1) where the C column contains the dates. Basically I say that the Index column should contain a 0 if the date is the same as previously registered, 1 if it is a new date.

The index column is used in some conditional formatting rules, so I would like to keep it anyway.

Example of the table:

Date         Val     Index   Sum
26.01.2009   167,1   0
26.01.2009    13,3   0
26.01.2009    58,6   0       Should contain sum of day
27.01.2009   233,2   1

It is in the Sum column I want this function. I need a function that does something like this (pseudo code):

=IF("Val" column.nextRow contains a "1") 
 THEN 
Summarize all "Val" cells from the current row and up to (not counting with) either the first blank cell or a cell containing "1")
 ELSE
Display empty string

Can this be done?