What would be the best way to go about summing values based on certain
criteria. I have many different spreadsheets that contain total customer
payments and total company payments for a given customer. When the total
customer payment for a given customer reaches a certain number (can be
different on each worksheet) that customer hits a "gap" and does not have to
pay until the total customer payments reach another amount (can also be
different on each worksheet).

For example the two columns being referred to would look like:

5 0.25
5 8.35
18 65.57
35 122.49
18 65.93
4.17 0
5 0
5 48.55
5 0.25
18 117.91
5 8.35
18 65.57
57.44 108.52
882.89 1535.39
5.25 0
70.21 0
73.16 0
13.35 0
135.91 0
83.57 0
5.25 0
83.93 0
165.96 0
135.91 0
13.35 0
83.57 0
165.96 0
73.16 0
5.25 0
13.35 0
83.57 0
165.96 0
83.93 0
5.25 0
5 92.43
6.33 120.2
2 7.3
5 85.81
2 2.4
5 85.81
5.37 101.98
5 21.29
5 92.43
6.33 120.2

How would I go about accurately calculating the first columns totals where
there is the string of 0's? That would be the "gap" period for this customer.
It will not be as simple as sumif. I only want to calculate where there is a
consistant string of zeros.

Any suggestions?