Showing Negative Numbers As Zero's

Assuming your calculation is represented by
%sum%, try this:

=if(%sum%<0,0,%sum%)
---a--- b --c--

a - checks if the figure is negative
b - the value to be displayed if it is negative
c - what to do if it isn't - the sum

Fill in A-1 throught 7 with each number
1
2
-5
-6
2
5
10
Now in cell B-1 type in =IF((A1*7)>0,(A1*7),"0")
Then you just fill down from B-1 to B-7
Example cell A-1 is 1, so 1 times 7 = 7 and
7 is greater than zero so its going to let it stay.
Example 2 cell A-3 is -5, so -5 times 7 = -5 and
-5 is less than zero so its going to put zero in there.

Actually instead of an array function u can just pop this format into the custom number format. That is under format cells, select the format number option than goto custom format and place this in the type box:

#,##0_);"0"