I do this through Excel itself. When you type 28/11/11 in the cell then I find it automatically converts to 28/11/20111. However to get what you want then on the hone ribbon click on the small arrow bottom right of number and choose custom. In the type box put dd mmm yyyy. If you highlight a whol column by clicking n the top before setting the format all of that colum will be in that format.
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