I have got a spreadsheet which has start dates in column A, end dates in
column B, and the value to be spread between them in column C. The dates
have been converted to weeknumbers using weeknum. Across the top of the
spreadsheet I have spread the week numbers 1 - 104 ( 2 years
worth ).Illustrated below:

Start End Value Weeks: 1 2 3 4 5 6 7 8 9
10 11 12
2 5 6
0 0 0
4 7 8

What I need to do is look at column A and B, look across the spreadsheet to
the corresponding weeknumbers in row 1 and spread the value in column c
between them (inclusive of the weeks in columns a and b) as shown below. I
have done this using formulae in a much smaller spreadsheet, however when I
try to do the same in this one it just falls over.

Start End Value Weeks: 1 2 3 4 5 6 7 8 9
10 11 12
2 5 6 6 6 6 6
0 0 0
4 7 8 8 8 8
8

The spreadsheet has approx. 9000 rows of data, in some of the rows, there
are no dates in columns a and b and they just need to be skipped over.

Any help would be much appreciated,

Thanks,

Mark