Lock cells after today date passed

I have here an excel sheet that has a progressive date from left to right column. A date is assigned to each column on the top. ( e.g.: 1/1/2012, 1/2/2012) Everyday after the daily data has been entered, I will like to create a macro that reads the date of each column (as assigned earlier) and lock the column which are less than today() (current date). Is this possible? Appreciate if you can show me how can this be achieved.