Excel 2003 How do I select every 6th cell in a column so that those cells appear blank?

I have two columns first column is month ranging from 2012-01 to YTD and the second column is values. I believe that adding the correct amounts of notes for June through access is turning up as an error because I have some values in celss for June, thus I want to make every value corresponding to 2012-06 blank. I attached an example so it is easy to see and yes the dates have to be repeated like that because I have names attached to those dates. Thank you for any help in advance!