Hi there, welcome to the board!!
I'm not sure how you're arriving at your "Pct Diff" or your "bills". But if you wanted to use a separate column, you could just use an IF() function. Also not sure what the value of the "Pct Diff" is. Is the 51 an actual 51 or is it 0.51, a percentage? Assuming it is a whole number, maybe you could use (also assuming the ranges go from A:E, data starting on row 1)...
=IF(D2>5,CommOfA,0)
Where the CommOfA is the commission of Sept 08, however you want to calculate it. You're very vague on what formula(s) you are using and how you would like things calculated. If you would like more information, please be a bit more detailed on your post, even think about posting a sample file.
HTH
